Smash Bros. appeals to people who aren't usually interested in fighting games, and as a result, the matches aren't always as competitive. But they have that potential. I have a friend who WILL win every time you play him. He's not an ass about it, he's just that much better than everyone else I know.
Fighting games practically require you to memorize obscure button combos to do well, something that I am simply incapable of doing. Best I can do in MK, Street Fighter, etc. is twitch a little, maybe throw a punch or two, and move very very slowly. Smash Bros. at least doesn't hide all the good moves behind crazy combos, so I'll give it that.
I suppose any game is going to come down to player skill. Smash Bros. is more in line with most other games while traditional fighting games tend to have the most stratification.