Question about the Siegelman case

In 2006, former Governor of Alabama, Don Siegelman (D), was convicted on corruption charges(http://en.wikipedia.org/wiki/Don_Siegelman). He had appointed "someone to a state board that the same man had been appointed to by three previous governors, in return for a contribution in support of a referendum campaign" (http://time-blog.com/curious_capitalist/2007/06/don_siegelman_and_richard_scru.html).

The (Republican) U.S. Attorney had seeked a thirty-year sentence, but got "only" seven years and four months - "less than the sentencing guidelines called for" (from the last link).

From the last link: "But sending a politician to jail for seven years for doing something that (a) was pretty much standard practice and (b) did not involve any kind of personal enrichment seems kinda, you know, wrong."

Question: How can something that is "pretty much standard practice" have "sentencing guidelines" calling for more than seven years?