I think admitting everyone IS possible. It's important to realize that these hackathons spend thousands to fly a lot of out of state hackers in (travel reimbursements). These hackathons will also send buses to nearby colleges, and even colleges out of state (e.g. anything within an 8 hour drive). If they didn't do those things (especially airfare reimbursements - kind of excessive if you ask me, or limiting buses to 3 hour drives) as much as they do now, they'd be able to narrow the pool a lot.