Well, most of the high % people are, in a nutshell, either (1) ppapanek type or (2) andyman type. The first category is ZOMG epicness -- whoever has seen the guy in action, knows his 70% are well-deserved -- there are but a few players of similar calibre with super-high stats; the second one consists of players that play almost exclusively on stacked teams.
That said, it is definitely possible to maintain a 55-60% ratio, provided you are solid (not amazing, just solid). Just don't get too adventurous playing with people you don't know, and try to be on host's side. However, given the small size of the community, I don't care to do it anymore. Someone on the team begins trash talking? Gg, I exit (now I use the wonderful enhanced squelch, too, but it's an example). The game lags too much and it started after 3 minutes in? Gg, hf. Etc., etc., etc. Well, when my % falls to ~40%, I'll probably ask my brother to concede a lot of games to me from my second acc. Just to keep it in 50% range -- believe me or not, there are naive people that do find some correlation between your % and your skill, and you want to be admitted into the games if you play at an unusual hour.