if every girl has boobs (nice or not), why doesnt every girl have an ass (nice or not), thats retarded, you just said two tottaly contrasting things there.  (as you said for the tits) it may not be a nice ass, but its there, if it wasnt, the couldnt shit, or get anal.
and why would you ever want a girl with huge boobs?  huge boobs suck!(no matter how nice the ass is).  they get to a point where theres nothing to do with them.  the biggest i like is around 36 C, bigger than that is just not fun