Since Linux doesn’t have Quicktime officially, just render everything as IFF’s. That’s what I do in OSX anyway. They’re almost as small as a Quicktime Animation, hold more info like Z-Depth, run faster in Shake, allow you to render a sequence across a farm, and if your render crashes you don’t have to start over. With that said, if I need a Quicktime, I just pop it in After Effects on another machine since any machine that requires a Quicktime file can convert my sequence to a Quicktime.
For a complete list of what you can export from Shake under Linux, just look in the FileOut node or help files.
To answer your other question, yes it’s a marketing plan on Apple’s part to sell more copies for OSX than Linux because they make the price difference back when you buy a Mac. The render nodes are free for a reason, they want to sell more hardware.