I'd be pretty pissed if I paid to rent this and couldn't try the online multiplayer without coughing up an additional $10. This model is obviously a big fail for those who want to "try before they buy".
I don't necessarily fault Blockbuster though, because it doesn't seem feasible for them to provide passes to every single renter. If they left the pass in there and the very first renter used it up, then all subsequent renters would be screwed anyway.
I think the game publishers need a free 1 week pass option for those who rent.