The responses from the boxing fans is simply showing that you don't understand MMA. An MMA fight can go to ground in the first second, but it can and does often remain a boxing, or kick boxing fight for the full duration.
A couple of things to note, MMA fighters wear lighter gloves... so the punishment you talk about that boxers take is a bit like being hit really hard with a cushion !!! but more importantly, in MMA, you can get hit by a forearm, elbow, shin, knee or foot in the face, and none of those are wearing padding.
MMA rounds are 5 minutes, not three - and i concede they don't go twelve rounds, but it doesn't take long for lactic acid to build up, and 5 minutes of getting an elbow smashing into your cheekbone is a long time.
In boxing, boxers can either hug each other for long spells, or backtrack and avoid getting hit. If an MMA fight gets into a clinch and not much happens, the ref will stand 'em up again.
Don't get me wrong, i love boxing, but i think it's time MMA got some limelight.