Unfortunately we have no info on this, but yes, evidently the Colbert Report's The Word, MTV News and Kayak.com apps have been pulled from the Marketplace. And that's just what we know of (anyone else see any others?).
Usually this happens because the app is broken, violates something in the Marketplace or perhaps the companies aren't happy with the app and what them redesigned (e.g. what happened with the Engadget app). It's even more odd since Colbert has been updated twice since its release, though it still shows v1.00.
We'll keep an ear out both as to a reason and if they return, but for now if you have 'em, best not to uninstall them.
Edit: Add 'Cartoon TV' to the list of missing apps and which we reviewed here.
(Thanks, SEKKDS, for the heads up)