I don't know if this is true (I'm not disputing it), however AppCode has officially been recognized as the only IDE version that will ever be compatible with *.xcodeproj files. It's functionality is not 'plugin-able'.

You're right, though I think that AppCode is an unusual case; you can only use it on OS X, right? It is a completely different beast.

For IDEA, though, you can indeed get the same functionality of PHPStorm, PyCharm, etc, by simply using their respective plugins for IDEA. However, the plugins are sometimes behind the stand-alone IDEs, in terms of features.