Problem of a ladders system is keeping it active, a live and interesting. Ladders are the hardest to maintain and least populair system for the competitive gaming world.

Cups are much more easy to maintain since they are a 1 time event. Not an on-going one like ladders. Leagues with seedings divisions might be a better solution. Since those are kind of a mix between cups and ladders. Plus it's more fair and you can base it on a season.

Battle.net has the advantage that anyone on anytime can play a ladder. Without to much trouble of a 3rd party program or website. Also, winning a ladder brings you big money and fame on battle.net. Which is ofcourse a huge motivation to actually play it. Last but not least is, is that WarCraft 2/WarCraft 3/StarCraft has litterly millions of people playing it. So the ladder isn't affected when groups of people leave or come.

I've seen alot of ladders going dead on ClanBase, ESL, CAL, TWL etc etc because a group of people didn't agree with rule changes so they just leave the ladder and kills it off.

example of a league:
Prime Group:
1
2
3
4
5 - Next Season demoted
6 - demoted

Group Alpha:
1 - Next Season Promoted
2 - Promoted
3 -
4 -
5 -
6 -
7 - Next Season Demoted
8 - Demoted

Group Beta - etc etc