Are you seriously going to argue that Tron has more of a mainstream appeal than pirates?
When's the last time a pirate movie lit up the charts? Cutthroat Island and Yellowbeard certainly didn't. Hook made pretty good money, but I think that had more to do with Robin Williams, Steven Spielberg, and the Peter Pan story, than the pirates. Even Disney's previous pirate movie, Treasure Planet, was a financial disaster. The PotC movies have made far, FAR more money than any other pirate movie ever.
Now, Tron certainy doesn't have more mainstream appeal than the PotC movies, saying otherwise would be patently ridiculous. Of course, up until the Curse of the Black Pearl hit the big money, it probably wouldn't be that much of difference between the two. However, that wasn't really my point. My point was the Disney has recently had pretty good success in turning weird ideas into multi-billion dollar movie franchises.
Again, if it bombs: whatever. If it make a ton of cash: cool.