..or just don't care. Also, if the UI is not built with animation / OpenGL support built in from the ground up, it might be a substantial job to add good support for it later on. OSX did all of this from day one, so that making an iPhone without OpenGL support was probably out of the question. I personally feel that the 3D effects in Windows and Linux feel grafted on "just for the fun of it", and I usually turn most of them off. But I never used the iPhone and felt that I'd do without the 3D effects - it will even sometimes drop the 3D effects in favor of responsiveness when it needs to, which i think says a lot about how much work they put into it.
Hardware accelerated window composition wasn't introduced until Jaguar (http://en.wikipedia.org/wiki/Quartz_Compositor#Quartz_Extrem...), which was, admittedly, early on in OS X's life, and the first version that was usable for most people. 2D drawing is still done on the CPU (outside of Core Image).
