Man is not impervious to corruption. That is why anything that man touches becomes corrupt. If you are looking for something that is not corrupt then there is only one place to look and it is not on this earth. With that being said that does not mean that someone will say anything to get what they want.
Everyone likes to talk like politicians are a different human race. They are no different than any other human being. Just like in religion you have those that feel they are more pious we have the same thing when it comes to politicians.
This is conversation for another day, but I'll give the 10 cent response.
To start, there's a big difference between those who seek power and those who are revered enough to be anointed (so to speak).
Additionally, I agree that politicians are as human as the rest of us. Many individuals would do no better than corrupt politicians, if they were put in the same position and given the same access to opportunity. There are also many people who would be better in those positions of power, but never make it there. Some shun the opportunity to begin with, in order to avoid playing in the mud. There are also many who lose out during the process, because they won't play as dirty as their competition. Ultimately, I do not believe that the best representatives of humanity are found in public office, though there are some exceptions.