The Times had an interesting article
Discovery Communications' web video strategy. Essentially they're going back in their vault and cutting up as much of it as possible into clips that are under five minutes long.
I've said to a few clients in the past that the reason to do something is that there's no reason not to. That doesn't always go over so well, but I think this is a particularly good example of that strategy. The cost of employing a few people to cut and upload video is lower than the ad revenue on the video they throw up. Even if they don't get rich off it, $1 is more than $0. (Though the article also points out that Discovery is a bit unique in that it has global rights to the content it broadcasts.)