These IDEs have an almost identical design language. I am at home in any of them and picking up new ones is pretty straightforward.
XCode 4 on the other hand has a completely different design language, and one that is limited in what it can do, but verbose in achieving it.
Limited, for example, because while I have a 17" MBP and a 23" monitor, I can't have the Project Navigator open at the same time as the Error Navigator. I can't view code and disassembly. I can't have code side-by-side in a split view.
Verbose, for example, because when editing a Scheme, it opens a custom, modal dialog, and if I press "Manage Schemes..." it rolls up and then rolls down another custom, modal dialog. If I then hit "+" it opens another modal dialog on top of my modal dialog. I thought we got rid of this kind of shit with VB6.
I've built a complicated IDE or two, and every time there was a custom, modal dialog, it was because we were rushed for time. Good non-modal design requires thought and effort. Flexible UI requires thought and effort. A simple, powerful design language requires thought and effort.
I would put money on XCode 4 not so much being "designed" as "rushed". Or perhaps "designed with lofty goals" - and one of those being "not like any other IDE, so that programmers learning on XCode will be completely thrown by any other tool".