Cheap sequels are a big money maker for Disney, which is why they churn them out. Pixar cares about quality. For example, Toy Story 2 was supposed to be a cheap Disney sequel (they had all sequel rights to the Pixar movies), but Pixar decided to make a real movie out of it even though it didn't count towards their six movie contract with Disney.
And IMHO, Toy Story 2 was even better than the first one. And the first one was incredible.