[EDIT]Holy cow, this thread goes fast[/EDIT]
@Feuerfalke
It's nice how you try to define openbeta and beta. But I believe you're also incorrect. In fact there are so many approaches to this - beta is just a popular term for quality assurance and in fact the typical approach for QA can be applied here. In fact it's more related to SQA (software quality assurance
http://en.wikipedia.org/wiki/Software_quality_assurance )
However, every company does it differently. Modern open betas are usually almost always just plain release candidates for example.
Personally I would say that it wouldn't make a lot of sense to beta the game using a public method. It's a niche product and it has very specific requirements. They can't beta with people like us because only freaks will actually join up.
So the question is what could they want to be tested and what requirements do the people who could test it have to fulfil.
In other words: selecting individuals would be way too much trouble and people would just claim stuff to get into the beta. However if they would just give beta rights to everyone who pre-purchases the game they'll end up with a ton of people who are most likely just in for the fun anyways.
If people are so eager to play the game early they do not have any discipline and thus are not the greatest beta testers anyways. So it's probably best to test everything internal. Remember how long this game has been in production! I can hardly believe that they will have a lot of bug fixing left actually.