I know it can't possibly be.
The downside is that I think RB's print options are way too limited.. for anyone wanting to sell a quality product.
Red Bubble hasn't cottoned on to the norm in business of treating your customers like idiots.. and avoiding blame at all costs. They have even shared their RB's sales statistics broken down into "pie" charts. Their prints and canvas prints are surprisingly low when compared to T shirts etc.. which just goes to show that buyers (including artists buying their own work for exhibition) are not using RB. So for me they are missing a huge chunk of potential business.
At Zazzle (which I don't really take that seriously as an "art" site) they have a range of quality papers and sizes.. up to "pretty darned massive". If you could combine Zazzle's print options with RB's youthful irreverence I think BubZaz would clean up.
Andy Mercer's Art
My Red Bubble - Art Prints
My Zazzle Shop- Cards, Mugs T Shirts etc