One of the complaints I've recently seen pop up consistently regarding Khan Academy is something to the effect of "Why should I trust this one guy? What does he know?" Prominent displays of Bill Gates helps to convince a random visitor of the site that, yes, this is a big deal and is someone you can trust, which is something a visitor otherwise couldn't possibly know until watching and carefully critiquing several videos. The wall of links is definitely important, especially the "wow' factor of the overwhelming number of videos, but without the proper context, that list of videos could look like a content farm, and a visitor might never be convinced to click through several links in order to see how legitimate they are.