That was true a decade ago but, starting around 2008 and forward, that's just not the case anymore. Macs are good and still popular but they are not what powers "virtually all pro digital music stuff" in 2012.
"virtually all pro digital music stuff is done on Mac"
Citation needed. I think this is pure speculation. Are you factoring in all the PC protools rigs in recording studios across the world? What about RADAR units? Or by "pro" do you mean "prosumer"?
Yes, most of the pro digital music production software is available for Windows and Mac (no linux): Propellerheads Reason, the whole Native Instruments product stack, Ableton.
There are just a few obvious Mac-only exceptions such as Garage Band and Logic Pro. Sadly none of the "industry standard" DAWs support Linux.
Since the death of the Amiga and Atari ST, virtually all pro digital music stuff is done on Macs.
But more musicians probably use Windows than use Linux.