There will be an OPEN beta, just like they had with Bad Company 2 and Medal of Honor. You don't have to pre-order to try the game before it's released. I would guess that the people who bought MOH and the people that pre-order BF3 on Origin will get to start playing the beta like a week before everyone else. It's a pretty stupid "exclusive bonus" they're offering because they didn't save anything for themselves.
I was considering buying from Origin because for a while it sounded like that'd be the only way to get the Physical Warfare pack, but I'll just order retail from GameStop. No matter what, you have to launch the game from the Battlelog website anyway.