Buying a Mac shouldn't be just an iTunes decision. With the new Intel chip based Mac, there is no backwards compatibility with any Mac programs that are not based on its X operating system. I am still migrating files over from my original eMac to the new iMac and some files have been rendered useless because not all software makers (especially for games software) have upgraded their products to the X os.
With all that said, Mac is still the way to go. Just not having to worry about viruses and spyware makes Mac worth it. If you have the original CD's, it may just be easier (but longer) to reload them into iTunes.
Also, do not go with the wireless keyboard & mouse options on the new iMacs if you are purchasing now. The keyboard performs worse than the mouse ... less than a month battery life; typing skips; etc. Apple is working on it.
Regards, Rich