Besides upsetting Sigma lens compatibility, it turns out that Nikon may be disrupting other accessory compatibility, too. The recent D3100, D3200, D5100, and D5200 firmware updates appear to kill two birds with one stone: third party battery replacements apparently don't work in the cameras, and Nikon batteries apparently don't work in third party battery grips for those cameras.
The conspiracy theorists are hot at work, with their bottom line being that Nikon is trying to kill off all third-party accessory makers in order to sell more accessories themselves. I'm not sure I fully believe that theory, as Nikon isn't exactly very efficient at making money off their own accessories. They're actually pretty terrible at it. Moreover, in the case of the battery situation, I suspect that Nikon's intent is first and foremost to support the new a variant of the battery in question, and secondarily to reduce product liability. There really aren't strong standards being enforced at all these clone companies in SE Asia doing knock-off products. We haven't had a terrible instance reported yet, but you only have to look at all the "died while charging iPhone" reports out of China to see the potential: cheap accessories with low quality control—especially when plugged into an AC supply—are a hazard.
A quick check of dozens of camera maker and third party batteries in my gear bins showed me that virtually all (though surpassingly not all) of the camera maker batteries are at least UL Listed, which implies passing controlled testing and agreeing to strict QA standards. Not a single one of the several dozen third party batteries I have were UL listed.
However, Nikon is no longer shooting themselves in the foot: they're aiming higher up the leg now. We're getting closer and closer to the "all Nikon" ecosystem as a result of Nikon's many actions with third party products. I've generally opted to point people to Nikon products for Nikon cameras in my support, site, and books. Even for lenses, where we've had a number of small compatibility issues, but more importantly, they also are simply differently colored glass that can impact white balance and color settings on the camera.
Nonetheless, I think third party participation in the Nikon ecosystem is healthy for everyone involved, including Nikon. That's even more true today now that we have a competitor consortium that has agreed to a known standard (the m4/3 group of camera, lens, and accessory makers). Moreover, both Fujifilm and Sony are known to be working with a number of third parties directly, too, especially lens makers.
Nikon can't win long term with a go-it-alone attitude. Imagine what happens if all the third party accessory and lens manufacturers simply stop making Nikon-related gear because of the hassle? You walk into your dealer's shop and what would you see? Worse still are the uninformed consumers. What do you think happens when they purchase their camera and accessories at Best Buy? Yep, the extra battery they get sold is a third party battery because it's far, far cheaper and with a better profit margin for the store. Then their camera's software gets updated and they go back into Best Buy and complain. Or worse, tell all their friends to avoid both Best Buy and Nikon.
This is the reason why smart companies such as Apple set up licensing systems with logos (and m4/3 for that matter) to indicate true, authenticated compatibility. They avoid the liability by being able to claim that you didn't use a licensed product with theirs should you shop the really low cost back markets, but they allow the ecosystem to build and become more than the sum of the parts by showing strong third party support, and support that even the Apple store will attempt to troubleshoot in most cases.
There's no way that Nikon is going to make every lens we shooters might want, even if they ever do get their act together and start plugging the holes and upgrading the full set the sophisticated user is looking for. So going-it-along means that Nikon will eventually start looking like it's missing pieces compared to other competitive products that have strong ecosystem support.
I'd go further and say that Nikon has never shown any clear competence outside of the camera body and lens. Take the WiFi nubs, for instance. To be truly useful, they require software on other devices. Nikon's software, like those of most camera makers, is terrible. Yet I know dozens of programmers who could do far, far better very quickly. Only problem is, almost certainly they'd be programming for a changing target with Nikon, and maybe even inhibited by things like firmware updates, so why spend the time and energy?
It really doesn't matter what the reason is behind Nikon's firmware move. The real problem is that Nikon is once again lowering the trust factor with its user base. These things are not only cumulative in the consumer psyche, but exponential. As in "fool me once, no big deal. Fool me twice, problem. Fool me three times, massive humungous problem. Fool me four times and I'll set fire to your headquarters." (Just kidding on that last one, but I needed something to clearly illustrate the exponential nature. I'd never advocate burning Nikon's HQ.)
Thing is, even camera dealers are upset about this change. Selling only Nikon-brand accessories means that you either don't sell any accessories to the customer or you have one heck of a well-heeled customer. A D7100 costs US$1100. An MB-D15 costs US$265. An EN-EL15 is another US$55. A Nikkor 70-300mm is another US$590. Boom, we're over US$2000. Sub in third party options other than the camera body and you save the customer US$360, a whopping 18%. You still make the camera sale, you still make your margin points, and if you do it right your customer is happy with you because you found a way to put everything into their budget. Their other alternative would have been to go for a lower body or skip the added lens. The really savvy dealer can talk you into the third party deal and then upsell you into getting the Nikkor lens instead of the third party one. But if the customer comes into the dealership saying "I heard that Nikon cameras have compatibility issues with third party products," any sale involving Nikon gear is going to be more difficult. I've written about "business frictions" before, but Nikon just keeps piling on frictions to their own success.
As for the third parties, they adjust. If Nikon thinks they've solved any problem with their compatibility adjustments, they're wrong. Sigma will fix their lenses to deal with Nikon's tweak. The battery and grip makers will look at what the new firmware does and adjust their products. It's possible that some third parties will evaluate whether or not they want to do Nikon products any more given the extra costs Nikon just threw at them to do business, reducing customer options when buying Nikon gear. What customers will remember is what Nikon did, though. There's a new friction to selling someone a Nikon: "Doesn't Nikon tend to break third party products intentionally? Do I really want to pay for having the Nikon name on everything in my bag?"
Call it the Nikon Tax. Only thing is, last time I checked, customers don't like taxes. When offered the choice of tax or no tax, which one do you think they'll take?
Bad move Nikon. Bad move.