SInce you guys mention about silva losing to mercer meaning a thing, have a look at this clip. An LIGHTWEIGHT MMA champ vs a SUPERHEAVY WEIGHT boxing champ....
In mma, the fighters must worry about take downs, kicks, elbows, knees, punches, subs etc. Their stance and defences will surely not be as "SWEET SCIENCE LIKE" compared to boxers as they worry more than just the body and the head.
Boxing is part of MMA. And yes, one punch can end a fight, boxing or MMA. But there are the take downs, knees, subs, ground and pound.. etc. which is major in any fight.
By the way, do you know how much heavier butterbean is than Geki?