Oh, I'm quite sure that politics and economics play into a lot of extraditions. If, say, an agent of country X commits a crime in country Y, and flees to country Z, then Z definitely has to decide which country they're going to side with, because there are legitimate diplomatic and political consequences to be had. It's normal and expected to take politics into account when the crime committed is inherently entangled with politics.
But this isn't some espionage or diplomatic case. This is a guy, who raped a child, and then ran away. If the French are upset that a child-rapist might be sent to prison (Because "Oh! He's a cultural icon! That means he can do whatever he wants!") then they're being ridiculous; there's no legitimate diplomatic or political ramifications for France. If Switzerland lets Polanski go to curry favor with France (Or anyone else, or for any reason besides the arrest warrant being illegitimate, or Polanski facing treatment that violates human rights) then they are not living up to their end of the treaty, and they are acting abnormally. Politics are normally in play when it's a political matter. But this is a criminal matter -- and Switzerland, bizarrely enough, sided with the criminal.