Do you think only app developers can decide the outcome of Android vs. Apple war?

It would be possible for them to, but it would not be profitable. If they suddenly chose to support only one of the platforms they would be missing out a on a large chunk of the market and lose a lot of profit as a result of this.

Time is the only factor that can really tell the outcome, with both Android and iOS growing rapidly it's all down to which of the operating systems remains dominant. There may come a time when one of them proves victorious, but there's no saying when that will happen and what will cause it to.

I would like to argue that "quality of all their apps (much better than the Android counterparts)" is a false statement. Sure, you can get some real dumpy apps on Google Play but you can on the iOS App Store too. If you took the Android version and the iOS version of a few apps, say, SoundCloud, I don't think soundcloud has any bit of a worse app on Android. In fact, it might be better because it includes a little player widget for my home screen even!

That said, to answer the question: Yes, sure they could. They won't though, because there are developers that love both platforms, Apple developers and Android developers. Though this is the problem with Windows Phone right now, not enough people are interested enough in the platform to take the time to make apps for it. The consumers are who really picks the dominant one in the market. It's what we buy. Personally, I like both but I'm likely going all Android for my next phone upgrade (My contract will let me upgrade June, 2014) unless iOS makes big moves from now to then. It's what we buy that affects it most.

I dont think it will come down to the app makers, there is enough developers, and enough quality apps on both platforms that they should be set.

Part of the reason for the appearance of higher quality on iOS may be due to the architecture and environment they are running on. The longevity of business will probably be affected more by the agility of their business models than anything else. Of course this will still require a product that people would want. By promoting those types of partnerships and the new methods of consumption, a business could survive the near future.

Small scale developers are already having a substantial impact collectively. When Valve Software opened the Steam Workshop they were quickly dwarfed in content creation by the mod communities. There's no reason why this couldn't happen with mobile development. I think it would be more of a social factor in that, there would need to be a large enough number of people with the skills and interest to bring it about.