Well yeah if you had to wait for apps to update before you could use them you'd definitely be annoyed, but the beauty of mobile (and desktop) apps is that users don't expect to constantly be running the latest version of a given app, which means you can slowly update large apps in the background.

When you visit a website you expect to always be running the the latest version of that website. In fact, most users aren't even consciously aware of the fact that websites have versions at all.