In my experience, at the under-grad level, the college you go to doesn't really matter (and especially your grades). I know that when I am hiring, I personally spend exactly 2 seconds looking at what school someone went to (and exactly 0 seconds looking at their grades).
It may be different at the post-graduate level though.
Yes, I suspect the elite-college job premium comes less from that mechanism and more from (1) more-skilled students applying to higher-ranked colleges, (2) unofficial/semi-official cumulative advantage processes whereby current students at elite colleges benefit from past elite-college graduates becoming elites in external social networks, and (3) elite colleges having better official career services like interview practice sessions, job databases, and careers fairs.
Some quick background, I am putting together a non-profit whose goal is to provide objective, rational career guidance to high school/college students, with the aim to solve what I see as a pretty big problem in the American educational system: our current career guidance is more focused on how to get a job on your chosen field, rather than what field should you choose in the first place?
Mid-ranged goals involve setting up programs where students can "shadow" people who work in a field they are interested in so that they can see what those types of jobs actually entail. Short-term, the goal is to put together some informational resources that students can use to help guide their decision a little more rationally.
One of these information resources is a database that uses data pulled from the Bureau of Labor and Statistics, to tell you