As much as I love Thomas Sowell, I'm going to have to disagree on this one.
The positions he's talking about are most oftentimes seen as a service to country, not a lucrative job opportunity. Just like ministers could get much larger salaries if they were to go into a different field, but they choose to serve the Lord.
Also, we the people select who we want to serve us. If we have a crop of "cheap politicians" serving us, well, we get the government we deserve.