[quote name='bigdaddy']But LEGO didn't lose it, they didn't want to continue it. Sets that don't have a vehicle in them don't sell well, and LEGO lost a lot of money on Spiderman.[/QUOTE]
I think it's also a matter of paying licensing fees. If Lego has to pay a license fee to make Batman sets or whatever, that cuts into their profits. If they can sell just as many units with intellectual property that Lego owns itself (say, Agents or Power Miners), then they make a bigger profit.
Of course, one would assume that the really popular intellectual property (i.e. Star Wars) actually sells a lot more than the Lego-created IP.