Yeah or another theory is that Nick will cancel SpongeBob in 2012 because they are scared like some other people that the world is gonna end that year. I don't think that's true though, the world would be ending too quickly and too fast and suddenly for us that year!
But really this show is just great being the original and not having no spin-offs (cough TSL had a Spin-Off too called TSLoD where I think its terrible cough.)
SpongeBob SquarePants is best staying at one show (the original SpongeBob) and running until it can hopefully rest in peace and have a good ending to it. Besides I still think its doing pretty good so I think it can make it at least another few years, I thought Sand Castles of Sand was good but I thought Toy Store of Doom was even better!