Well normally ladders are run continuously, i.e. - there aren't any 'seasons' to it. If you are ranked #1, then you are as good as there is until someone dethrones you.
TWL DOES have the capability to run leagues, similar to cal/sta/etc, the league system does have a playoff system as well as All-star balloting system built into it as well. I considered hosting a Urban Terror league, but with CAL and STA (among others) I think UrT may be a little saturated in the league department. The TWL league system is really nice, and you just sign up for it using your existing team, so technically TWL has all the goods you need in one spot.
Now, if I can get Drac to close up shop on STA and move everyone to a TWL league I'd be all over it ;D
Wolf 7v7 league page:
http://www.teamwarfare.com/viewleague.asp?league=RTCW+7v7+Beta