You used a Nelson site to determine he was a moderate?
Now look at the ACU on conservative issues for Nelson:
Bill Nelson D 4 20 14 4
It was 4 out of 100 in 2004 and 20 out of 100 for 2003 with a score of 14 right now. They don't have 2005 up yet but only getting a 4 out of 100 in 2004 -- that's almost as liberal as they come IMHO and not even close to being a centrist.