In other words: Connections and reputation. It lets you market yourself better and meet people you wouldn't meet otherwise.
If our recruiters' actions are any indication, a name-brand school can save your resume from being trashed right off the bat. But it won't land you a job; it just makes the competition more intense.
In general, restricting your candidate pool based on where they want to school probably really improves the signal-to-noise ratio. And since recruiting is a numbers game anyway, with dozens or hundreds of applicants applying to each position, it's not exactly an illogical thing to do.