That's how I played sc1 + bw too. I was addicted to UMS, but never played sc1 ladder at all.
Sc2 got me into playing the actual melee games, and laddering and such. But I just find it a chore to play the sc2 for the melee, it just takes the fun out of the game.
So I've reinstalled sc2 to play solely for the arcade especially now with the updates to it. Am I crazy/panzy for doing this? I just find arcade more fun, heck probably just as addicting as sc1 ums. Just how many players play the arcade compared to ladder?