Weeeeee, once again Slate to the rescue. There is a good reason the Democrats wouldn't put him on the ballot and Comedy Central wouldn't like it either.
It is all about the candidates having equal access to the public. NBC has stopped running Law and Order re-runs with Fred Thompson.
http://www.slate.com/id/2176466/"If the Comedy Central host follows through with his bid and continues to use his show for political self-promotion, does he risk violating election law?
Yes. The Federal Election Commission prohibits corporations from making "any contribution or expenditure in connection with a federal election." A "contribution" includes "anything of value," including airtime. Thus each time Colbert promotes his candidacy on The Colbert Report, he'll be accepting an illegal "in kind" contribution from Comedy Central's parent company, Viacom.