http://online.wsj.com/article/SB10000872396390444246904577573531064431936.html Apple claims the license for its default YouTube app has expired and it will no longer come per-installed on iOS however google says it's working on it's own appstore app. Luckily google has been putting out some good apps/updates for iOS lately so the extra step to get it doesn't bother me.
To be honest, I won't miss the old app. Really, it wasn't that good. Google is making a new app, which, I hope, will be better. Not many people use the default app anyways, they rather use the Safari website or ProTube.
