College recruiting is pretty important for Facebook, Google and Microsoft at least. In programming world "previous job experience" is a bit vague, as contributing to an open source project or building some non-trivial Web/iOS/Android apps is not "job experience" in classical sense, but adds significant bonus points to one's resume.
At any rate, those are "lowest-level" SDE jobs available at such companies. They hire _many_ recent grads with nothing but a few internships worth of experience too.