I don't think that it's just because they like it. This would actually belittle all the work and effort that Apple designers put in their great work. In my opinion there's alway a reason behind Apple's design choices, because everything is studied with the highest attention and care for details, from the general look to the apparently insignificant details. That's why the Mac OS X User interface is regarded as one of the most beautiful and perfection-aspiring ever. And you get the idea of this beauty and attention in every single little detail, from the "traffic lights" buttons, to the system icons, like the "textedit" icon hiding the "Here's to the crazy ones/think different" text. And the new Lion "about this mac" panel makes no exception.
I just hope I cleared that...