facebook’s freshman thirty (widgets & apps, that is)

Mashcode’s got a list of facebook apps right here…and it’s a classic case of taking the API and making it available to a great set of services–Feedburner, College Humor, ilike, dogster–there’s plenty for everyone.
Isn’t there an obvious question here why other networks with larger user bases haven’t developed their internal APIs in a way that would fuel this kind of development?
And another question about whether facebook’s investment will accelerate that movement?