When an employee violates some part of the employer's code of conduct or some aspect of a work contract, it's not automatic or inevitable that s/he will be suspended or fired. Sometimes the only consequence is a reprimand. Often it's a fine or short-term suspension.
Even if Olberman's having donated a relatively small $ amount (in the context of national politics and well-paid public figures) to some political candidates violated his MSNBC contract, I'd say any suspension beyond a day or two is overkill.

Anyway, Olberman fans quickly circulated a petition online and got over 300,000 signatures in just a day or two, and MSNBC promptly reinstated Keith.   That makes sense, both in terms of the ethics of Olberman's actions and in terms of ratings.

And, oh, Mark S, MarkS, Olbermann donating to Grijalva's campaign right after Grijalva appeared on his show doesn't suggest a quid-pro-quo to me.   If your interview with a candidate convinces you to back that candidate, where's the quid pro quo?
And do you think political candidates have to be given any incentive to appear on radio or TV -- especially in a non-hostile venue -- other than just the chance to get the air time itself?