The closed beta access comes with a couple provisions. You'll have to specifically pre-order through Perfect World to get beta access, as a Steam pre-order won't reap the same results. Also, it's important to note that Runic Games says that the "exact date of [beta] access will vary."
Runic Games is a subsidiary of Perfect Worlds, which also owns Cryptic Studios.
We found ourselves incredibly impressed with Neverwinter after getting our hands on it at PAX East, so it's great to have a guaranteed path into the beta. Make sure to read up on our impressions of this upcoming title from Cryptic.
[Thanks to Jay for the tip!]