My annoying use case for those was ebook readers - I have a pretty massive library of epubs (Thanks Baen Webscriptions!) and have tended to just dump a ton of them into a folder in storage on a device. I can then pull those up in CoolReader, Moon+ Reader (position sync!) or FBReader as I desire. On Windows Phone every reader app (not that there were many) had to have its own independent download because god forbid you have shared freaking storage.
Somehow I feel that this is also going to end up hitting things like third-party gallery apps such as ones that allow tagging, along with the multimedia stuff that other folks are concerned with. Oh, and music. The death of MP3s saved locally to a device and used by multiple apps?
So much of what Google has been doing with Android (turning it into a minimal platform for running the massive Google Play where all functionality lives) seems like they're heading down the walled-garden that Apple has always been, but with creepy monitoring and ad-driven revenues layered on top.
I always dismissed iOS as an option because I didn't like how locked-down it was and I really liked swipe-based input, but now that iOS allows keyboards and the locked-down aspect is happening everywhere perhaps it's time to reconsider.
Edit: removed disparagement of Windows Phone apps