Aside from the personal consultations, experience, expertise, and connections that YC offers over Kickstarter (which are all vastly important), I suspect it is

Aside from the personal consultations, experience, expertise, and connections that YC offers over Kickstarter (which are all vastly important), I suspect it is much more difficult to raise funding through crowd funding than through angels & VCs, relatively speaking. There's also the question of whether or not they'll know how to most effectively use that funding. Consultation from experienced people like those at YC would help there too. Diaspora is an edge case. All the press they've gotten have catapulted their popularity enough to raise this amount. And more power to them too; they have a valiant goal and I hope they can execute on it well. But I wouldn't try to raise funding for a for-profit startup through crowd funding, unless perhaps your startup has an apparent, believable, and widely-desired benefit to society. I'd love to be proven wrong, but this argument only has a sample size of 1 so far.