I agree its a cheap way to win. Like someone else said, you have to carefully read the settings before you join a league (and hope the commish doesn't change them before the season starts- one of my leagues was changed from Rotisserie to Points after the draft and before the season).
In my Rotisserie league the commish dropped the max games limit (also after the draft!), but no one in this league has done that. I was in the lead all year, but now my lead is down to 5 points so I'm getting nervous.
In my H2H leaugue, some guy decided that come playoff time he was going to churn his players every day. His rational was that he hadn't maxed out on the # of moves allowed for the SEASON, so it was ok. He eventually got locked out because after some people protested, he said some stupid things in the messages and the whole league turned to chaos.
The best way to avoid this in my opinion is to have max moves or max moves per week. In H2H leagues it should be agreed before hand that the max moves will be changed for the playoffs (a few per week for instance) to prevent churning.
Churning sucks. It takes the fun out of it. Its mindless and it favors people with too much time on their hands. I spend a lot of time everyday checking my lineups, but I don't want to spend even more time looking for playes to pick and drop just so I can keep up with the Jone's.