This is a fun explanation, but I don't think it's true. John McCain is treated as an expert on many budgetary issues despite having no clear understanding of them. Olympia Snowe doesn't strike me as dim, but she's often treated as having some high principles of moderation even though she pretty much just wants to split the difference between the two parties. Bob Kerrey famously wandered around the Capitol deciding whether to vote for Clinton's first budget and was heralded as a sage for it. You don't need to be a Jew to get an undeserved reputation as a wise thinker in Washington. Being a centrist or a maverick is often enough. Lieberman fits this media narrative nicely.