I imagine a lot of what they produce comes from simply being a great artist. There are certain aspects of art that you can learn and certain crafts that can be done quite well without truly being artistic.. but I find drawing from scratch and creating realistic elements, etc something that you are just born with. You can learn to be an accountant or a doctor.. but the arts are highly innate abilities that typically require something other than taking a course or following a tutorial. I take great photographs.. and can churn out some great looking fine art prints.. that's my "art".. but I can't sit down and draw a scene in front of me.. to me - that's just something you either can or can't do. I can draw something amazing now and then.. but I consider it more dumb luck than any ability.

Designers.. what do you think.. it is an interesting question and with the advent of computer graphics and the software out there (3D graphic programs, photoshop, modelling software, home design), perhaps the line is being blurred a lot more.