If developers believe this technology will be important in gaming, then they will want a dev kit as soon as possible to remain competitive. Note that Sony, Microsoft and Nintendo sometimes charge for their dev kits.
The dev kit isn't just an SDK - like console dev kits, it includes the hardware. Giving them away to anyone who says "yeah, I'll totally make software for that" doesn't sound like a brilliant business plan.
Actually, that is a valid tactic, if you are having trouble getting your hardware to gain mindshare.
For this, though... Well, it's already over 3x its initial goal and shows no signs of slowing. They absolutely made the right decision to charge for the devkits. At least, to the plebs, like me.
Higher level developers (i.e. famous names) probably will get a kit or 2 for free still. If Carmack wasn't already part of it, he'd be one of the names I'd expect to get a free kit.
"I've been thinking of buying a new car. Pledge to give me $500 to help me buy my car and I'll send you a t-shirt with my car's picture on it."