I must be reading the contract extracts incorrectly, because I thought DLP had to pay TWDC each time they have different characters (therefore they don't bother) but the way I read this it seems to suggest that they pay a %age of the take each year, not linked to which characters they have.
But if that were the case, surely they'd have loads of different characters all the time - of course, the ones they have are great, but we have met them a million times and new ones would make trips to DLP even more appealing.