The company is hoping to have both channels signed up by the time the Hulu subscription service hits.
The success and failure of the Hulu subscription service is directly dependant on the shows it can offer. It needs popular shows that people want to watch, and lots of them. That's why Hulu's working with both Viacom and CBS to secure a bit of programming.
Viacom, the folks that own MTV and Comedy Central, pulled both The Daily Show and The Colbert Report from Hulu back in April, and the site's visitor count has dropped significantly. Hulu wants them back, and with good reason.
CBS, on the other hand, is the only one of the four major networks that doesn't own a piece of Hulu. Adding CBS shows would be huge for the service.
Source: Business Week