Your thread title is a bit misleading.
I thought about "desktop picture sets" first when I opened the thread, then when I read the first line, I was thinking about "PC desktop computers" - and then, finally, I got what you were getting at.
Well: I personally think that people _should_ be free to choose. Some of the keyboard/mouse combo packages look really nice in stores, and before the Mighty Mouse, Apple didn't really offer a good mouse.
However: I don't like combo packages in this case. A good keyboard is very important to me. (And "good", with keyboards, seems to vary widely depending on the user...) So is a mouse.
The problem with PC keyboards often is that two or three keys are differently mapped. So I'd first try the Apple keyboard(s), and if they're okay, why not use those. Mouse-wise, I don't think Apple has a really good thing going on. Mighty Mouse - to me - looks like a neat idea that often doesn't quite work in the real world.