Why? If someone is great at their job, why force them to stop doing it even when everyone they represent wants them to do it? If people get worse the longer they're doing their job, then since they're elected, the voters can simply vote for someone else. There's no need for some arbitrary limit when the voters get to choose.
I don't believe that these people are representing the people that voted them in, but because Americans in general are lazy, and tend to be apathetic, and sheep-like, and will vote for anyone in their aligned party, these people have realized that they can exploit their power, and use it to serve themselves. Hopefully my generation will change this, though, so far, the majority of my generation has only fallen to their knees in worship of the Obamagod, (he uses a BLACKBERRY, and is YOUNG, and has a MYSPACE, OMG!!!!! I SHALL FOREVER BELIEVE EVERYTHING OBAMAGOD SAYS), so I doubt anything beyond the normal two-party bs will happen.
Because of this exploitation, perhaps a term limit should be enacted, if only to save the American people from their own laziness, and apathy...
We have only ourselves to blame.