I think you would be very surprised as to what does and doesn't sell on CafePress. Are they doing as well as you are, I doubt they are, but are they doing anywhere near the work you are, no way in hell. They are likely targeting an entirely different market than you are. You're going with viral marketing centered around Facebook. CafePress is largely populated by middle aged women. I would guess the cross over for those two groups isn't that large.