This is purely anecdotal evidence but many of the elevator pitches I saw were from companies and individuals that were adapting their ideas to the fb app paradigm. Facebook is a great distribution channel for any company really, especially when they are giving you a 25,000 dollar grant to build on their platform.
I discovered YCombinator several weeks ago in a blog post about the fbfund/YCombinator meetup written by a July 2008 fbfund recipient. A link was posted prominently on the fbfund Facebook page for at least 4 weeks. This was the only centralized place for fbfund discussion and updates so a lot of applicants checked it regularly and may have found their way to the YC website.
Maybe the demographic data destroys that theory though.
