Actually, at the moment, given your example, you've got it backwards. Getting ito the ecosystem is what costs you. You have to re-encode your video files.
Beyond that, every other ecosystem is pretty much the same. If you went from Android to webOS, you wouldn't be able to bring your apps with you. (I'm not sure which forms of DRM those to use, so this next statement is conjectural) And movies that have Android DRM aren't going to play in your webOS player. Etc. And the same is true if you're moving from Android to iOS. Or webOS to Android. Or webOS to iOS. Or iOS to either of the others. Or to or from QNX(?) on the BB PlayBook.
The point is, if anything, iOS is actually easier to get out of than into, for precisely the reason that you cited. If anything, because of the preponderance of devices running iOS, it is easier to move your content around, both DRMed and non-DRMed, among your devices, if you are in the iOS ecosystem.
And, incidentally, the iPod, iPhone and iPad can play XVID files using VLC.