The thing is, Janna: they can sell a new EP for $40 a copy. The patches are given away free. As far as EA is concerned, their priorities are just right - they're not in the business of making gamers happy, they're in the business of making money. The only way to make EA focus on patches instead of new EPs is to stop buying the new EPs and let them know it's because they keep breaking stuff and not fixing it - and it's more likely that if we did that, they'd stop work on Sims 3 altogether because it's no longer profitable. They'll do approximately the minimum amount of patching needed to keep us spending money. (I'm actually astonished that they put out a separate patch to fix marriage, telescopes, and space rocks, and how quickly they did it.)
I think to some extent they're relying on the modding community to do some of this for them. There are easy-to-fix bugs that have stood since day one of the base game release - like the one where working out at a gym is slower to gain athletic skill instead of faster, because a constant that needed to be 2 was 0.5 instead - and meanwhile I know there are mods that address some of the complaints, so they feel that anyone who feels strongly about the problem can download a mod...