I'm going to make this short and sweet. People who donated years ago get early access to the game. There wasn't very many, so no problem. Now picture this, what would happen if it opened up to the thousands of people?
First of all, the game can't handle that yet. A few days ago, there were only three servers. Luckily, progress is being made. I think I saw 15 today.
You will get the game eventually. The wait is worth it. Trust me. Bethesda and Valve take their time, and their games are superb. It's just taking its time. Dinosaur games have a reputation for being bad you know? It NEEDS a good launch.
Release dates are EXTREMELY hard to put on these things, so I would expect it by mid-late October. Don't assume any earlier as there's a chance of getting disappointed.
If you want to see more of this game, I have a channel full of footage: http://www.youtube.com/user/BlueRexRage?feature=mhee
..and my Steam account has a ton of screenies.
If you have any questions that haven't been answered by this piece of text, feel free to post, although I may not have the answer. Since I'm not a developer.