The haircut part is about not having to leave campus and go do errands on a weekend, so your weekends can be about having fun (or more realistically, doing more work for the startup ;-)). It's actually pretty handy, being able to tuck away a 20-minute haircut appointment in between two meetings.

There are also laundry (Facebook), massages (Google), mini-day spas (Microsoft; maybe? private to employees but not clear on pricing), etc. Haircuts are very much in theme with "work and live on-campus" approach.