The common denominator apps for Web, Twitter, Maps, Angry Birds, MP3 player and whatnot are basically equal across platforms. You can easily adapt to the peculiarities of one, so that the familiarity becomes an actual asset. Differentiation is then minor preferences in form factor, UI idiosyncrasy, etc.
But when you get to serious applications for music recording, editing and processing - or astronomical observation - or organising a rock climbing expedition - or any other rather specialised pursuit?
iOS is really the leader space. Because the tablet really is all about the apps. I can do everything from replace a 4-track studio to manage XBMC/Kodi, before a jailbreak. Nobody bothers with this stuff for Win or Droid. They seem destined for Spotify not Garage Band.