look at crocop and the success he's had with powerful legs, his upperbody really isnt that big for a heavyweight. but then on the other hand many boxers have matchstick legs compared to upperbody so i guess it depends. id say legs for all but perhaps not boxing!
boxing is soo not upper body. neither is wrestling, actually. in applying submissions it might be, but in controlling your opponent lower body strength is more important. lower body strength is what gets you off the bottom, too, if you're there and don't want to be.
oh come on. have you seen any of tito's leg workout on all access? don't be fooled because he's got those birdy calves- his legs are are strong as the rest of him. i bet you he's stronger in the legs, proportionately, than he is in the chest.
and rampage's glutes and core are diesel (may be gay to use this word, but in this case it fits). i bet you he could put up 500+ in a squat. that's pretty strong, in my book.