As a student, and a startup employee, I must say that not everyone has the ability to expense their employer.
Most conferences have different pricing tiers to deal with this stuff. Seeing as how this is Github's first conference, if enough people bug them they might do something about this.
I've found that most conferences with such a low limit of seats tend not to have student pricing tiers, but I'll bug them, couldn't hurt.
He must be self employed.
I'm not self employed, I work for gdgt. I just wish I didn't have to bug my employer to fund me attending this kind of stuff and would much rather pay for it out of my own pocket because (personally) I tend to care more about something if I'm paying for it out of my own pocket.