He actually might still be their uncle, a widely supported fan theory going around is that the "Stan Pines" shown as having died was Stanley Pines, not Stanford Pines. In which case Stanley is probably their grandfather. Either that or Stan's really their grandfather and not their 'Grunckle'...
I don't think of it as the name of the place. I think of the title as saying that gravity itself falls, which would be extremely weird, just like the rest of the show. Might just be me, but still...
