You DON'T need battle.net account with diablo3 beta AT THE MOMENT. You can log in with ANY battle.net account. It might be a bug or some hidden open beta but there are no official announcements on battle.net forums yet (aka "blue posts") about this, but the thing is AT THIS MOMENT you can play with ANY battle.net account. Don't know how long it is going to last, maybe they already fixed it.
Blizzard pages dont say anything about open beta, dont ever use anything that is not from their site, means ending battle.net or something like that (use brain), other things are just a way to screw you... i know the game might work, but usually at a cost of a virus that can like keep track of what you type (passwords), screenshot your monitor, download your files, ... or do harm