I think both MS and Apple will clamp down on many applications on the desktop. They are both pushing locked downapp stores for desktop. Apple continue to ban anything that competes with them on iOS, so I do not believe it has anything to do with battery life - in any case does the mobile version of FF use more power than IE?
Also, its not just phones, this OS is for tablets, and maybe low end netbooks, and those are not just turnkey appliances (and I think even phones are becoming less so).
Good news for Apple and MS, as their control on the software market on the platforms increases and it becomes accepted as the new norm, bad news for other software vendors and customers.