Honest question here because I don't know. Did Apple notify developers that certain APIs they use will no longer work in iOS 7 or cause the application to crash? If so then the developers are to blame. If not, then Apple is. I don't know what backwards compatibility Apple provided in iOS 7. The third option is that iOS 7 is buggy.
Um, have you ever logged into the Developer section of Apple's sight? It says what APIs are deprecated, has videos and documents on transitioning to more modern APIs, change logs that point out known bugs, etc. This talk of "backwards compatibility" is a bit confusing because each version of iOS isn't a complete rewrite (very few OS's do anything like that).
It sounds to me like you don't know anything about software development but still known enough to consider iOS 7 a buggy mess. That doesn't make sense.