This is a bit of a sticky issue... Those icons are licensed by Apple or Microfost... and I know that when people started to copy the iphone themes, Apple was threatening to go after them because of it.
Still, does that stop anyone from trying to make a few bucks? They will do it anyway until someone tells them to stop,... whether or not it's right or wrong.
Be your own judge. Personally, I dont think people should sell themes unless they theme ALL aspects of the theme themselves, and this includes their own icon design. Just throwing a layout together using someone elses artwork IMO should not be sold for profit.
The exception to this would be the commercial icon sets that you can purchase, and when you buy that set you have the rights to use it for commercial purposes (for profit) and there are many out there, some of them awesome if you are willing to pay.
Also, if you create a theme and offer it for free, but people donate for you to customize it for them etc, that is ok as well because you are not charging for the them, but for your services.