Now in the professional realm, PShop makes sense to have a Linux port. Strange thing though - a huge percentage of professional CG work is done in Linux nowadays, and has been for awhile, so I'm surprised that it's taken them this long to get around to it.
For computer generated graphics custom workflows and creating tools to animate things others can't have has been the driving force. There's plenty of complex interactions between models, textures, animations, physics simulations and various like creating a whole army from a few parameterized models and AI. No tool does everything well and often there's some secret sauce you want integrated into the workflow. Photoshop on the other hand mostly seems like a one-stop shop, you hand a skilled person the image and what you want done and he'll produce an end result. Efficiency seems to be the primary driver, not integration or customization.