Nobody. Creative people use all sorts of things. As a product though the Mac pro targets (not exclusively or exhaustingly) a section of creative professionals:

Nobody. Creative people use all sorts of things. As a product though the Mac pro targets (not exclusively or exhaustingly) a section of creative professionals: designers, music industry people, video editors. The design choices & margins produce a price that basically targets a 'need what they need regardless of price' segment. They've been doing so for a long time. In the Apple dark ages these people were a big chunk of mac users. You can still see the vestiges of this heritage in modern macs, eg iLife: Consumer versions of what their professional (in that space) users use.