I imagine it has something to do with companies not wanting video coverage on any other site than youtube. That way they can call a copyright strike anytime they fancy it. Can't exactly do that for Polygon or Rev3 videos, can they?
@lkpower: It depends on what Bethesda does with Fallout 3. It would be nice if they would patch out GFWL and add steamworks support to it, but for a lot of the older titles that had GFWL it doesn't seem likely.