I think I wasn't alone when, about ten years ago, I suspected Apple was working on a high-end image manipulation application along the lines of Photoshop. Just in case Adobe pulled the plug on the Mac version. My wild guess: Apple never needed to pull the trigger, so it kept improving it in secret. Apple still doesn't need to release it, but there's no reason not to either. Personally I don't use that kind of software but that won't stop me enjoying the sideshow.
I can't blame them. BUT I wish it were not so. They haven't lost money on their pro stuff (apart from maybe the XServe) so what is the harm of keeping it? From Apple's perspective, it's at worst - at worst - philanthropy which makes a profit.
EDIT: Apple will update the Mac Pro but later than customers would like.



