Not supporting Mac users is simply a very wise use of in-house resources.
Supporting the Mac means writing a version of the Zuneware for Mac, for starters.
As pointed out, that amounts to at most 4% of the market in return for a doubling of development costs. It means dealing with the headache of filtering out Fairplay files and explaining to customers why their iTunes songs won't play.
And since Mac users interested in digital music probably already have the "perfect" device and would only sneer at any lesser product anyway, it is a waste of effort to even try to reach out to the iPod crowd.
And finally, in the unlikely even anybody on a Mac had any real interest in Zune, as opposed to trying to make a point about lack of Mac support, they can always go to their Windows environment with boot camp.
Most of the folks who complain that product XYZ doesn't support their platform are more interested in complaining than in actually buying the product.
MS has made it abundantly clear that the target audience for Zune is young, hip, and un-Podded. That does not in any way describe the online Mac users that are complaining.
