Suppose you want an app to play videos. If your app uses a custom format no problem. If you support an open standard, the file might not, it might require more processing power than you have, it's probably for a different screen resolution, it...
In the end tech people are willing to trade stuff breaking occasionally for flexibility, but most people flip out when stuff breaks.
PS: I think you can break it down as do you want a VCR to show a movie to your friends, or a VCR that gives you an excuse to tinker.