I don't think you have any idea of what "limited play time" is, Annatar. Since the game's release I had time to play through the campaign on normal (that was ~3 days), unlock Zeratul's portrait, gold the challenges and do ~20 practice matches. That's all that I managed by playing every time I had the time for it and this is halfway through my holidays, mind you. And now I am going to enter the ladder and have fun, regardless of whether someone jumps ranks above me because he plays more or not.
Ladder play for me is about playing with people who are trying to win (unlike in Custom games where most of them don't really give a crap), who are on my level of skill and in a competitive (i.e. fair and even) setting. Not about competition per se, not about trying to squeeze my brains and fingers into beating the other guy and getting to Top1 diamond like it was a life or death matter, but about playing a fair game and having fun.
It's a game after all.
When I want to play SP, I play SP. When I want to play a Custom game, I will. When I want a fair match with someone of my skill, I roll a ladder game and I don't give a crap if it's counterproductive. That's what I find fun.
Anyway, suit yourself and have fun. I guess that's why they stuck so many achievement points into that game, so that people who want each and every one of them can have their hands full for a long time