Makes sense when you put it that way.As lame as this is, I think they are just really good friends, almost brother and sister type thing, and just like working together.
Plus other actresses know Adam Sandler movies have gone WAY downhill and shes the only one he get to be in them with him.
Edit:
Shit, put actors at first and I hate that crap. Dude is actor, chick is actress and I was talking about chicks, man.
I've always wondered about that though before, it seems like it's always her, although I think he did do a couple of movies with Selma Hayek if I'm not mistaken?