Let's look at it this way: the ratings of Congressmen amongst their constituents is usually quite high while the overall performance of Congress is very low. If money bought everything and the decisions it helped influence goes directly against what the people want, shouldn't the constituents be constantly changing their man in office? Not so much, as it turns out. Even though money does buy airtime for these guys, it is still up to the people to cast the vote. (http://www.opensecrets.org/bigpicture/reelect.php)
This can mean either two things. One is that on the small issues such as pork barrel spending, the people are very satisfied. However, when it comes to the big ticket items such as defense, we're not so satisfied because it requires a group decision. So if a district's congressman does a lot for his constituents but is one of the votes that goes against what the people want, most people are willing to overlook that one vote when they compare it to all the other decisions he's helped make.
The other one is one that I also agree with: that we cannot stand each other. Congressmen are surrogates of a collective opinion and even though, from district to district, Congressmen continually are reelected at high rates, we dislike the Washington gridlock. Think about that. We approve of our own Congressmen and despise it when other people stand in the way. And everyone has the same mindset!
So when you say that there is corruption in government, I do not disagree. However, I would not go as far as to say that every congressmen is corrupt because of their high retention rates. Those little decisions that people tend to overlook because of the benefits they get by reelecting someone add up. But maybe the inability to pin them down on it is our own inability to give up some of what we get and to listen to one another.