This is my 3rd (or is it 4th?) pre-order beta game from Stardock and they used this same pre-order beta system, and they have done very well right out of the box apon release. There was few issues apon those releases (especially compared to most other games) and have a rock solid community that has been very effective and keeping them on the golden path.
Those games I talk about are Sins of a Solar Empire and Galciv2:Twilight of Arnor (I can't remember if Dark Avatar had a beta; but I remember pre-ordering it).
I have also participated in open, and semi-open/semi-closed/closed betas as well (Roughly 12 in total, not including Stardock's), and all the games with a large or large-ish beta community tended to come out pretty buggy and balance being lopsided (Company of Heroes: Opposing Fronts is a recent example), while smaller community, like that for Act of War: High Treason (and Direct ation, but I missed that) had an opposite effect. Granted, there are exceptions (Lost Empire Immortals), but generally, in my experience, larger beta communities, especially when theres no tie in (like the pre-order), do not exactly beta as well.
Right now, the pre-order for beta system is working, and I don't think it should be changed.