Since when do people take South Park comedy for fact?
It's only as addicting as the person who plays it makes it. The game is set up so that before you reach level 60, you don't have to be online for more than 10-20 minutes at a time to make good progress. Only when you reach 60 you will have to choose between this loose style of rep questing, or a more time consuming raid schedule (4 to 6 hours at a time, once or twice a week). It's still managable though, no one is forcing you to keep playing for that long.
Also, CAMAROBOY69, it's not 20$ a month, but 14 or 15 (12,99 Euro here). That's pretty much the norm for MMO's, most companies need that kind of income to keep the massive servers running and keep 100+ people fed to keep developing things for the game as it goes on, the game masters to keep people in check, etc - You might be looking at hundreds, maybe thousands of people for one game just to keep it running 24/7.
Xbox Live is just running on a master server like setup (like the master servers you connect to to get server lists in game like CS, UT or Quake), and provides content at a one time basis (you just download it once and it's done) - the requirements on what the servers actually need is a lot lower, for example, there are at the very msot 5 people working at actually developing xbox live, and no moderators (game masters) are needed to regulate gameplay. Everything is automated.