Birk,
as you noticed, this is an upgrade (in this case more of an update) of DVD Architect Pro 5.2, which is only bundled with the regular Vegas Pro. Unfortunately this is not available to Movie Studio and DVDA Studio owners, in fact no Pro updates are.
A Studio upgrade may or may not be forthcoming some day, but judging by this release I wouldn't expect many significant improvements there either.
.
Seriously, hold the line? Yes, maybe there is reasoning there - but keep in mind this is really version 5.0b in new paint. There have been no bug fixes and no major additions of features that are useful for the greater client base. All users of licensed version DVDArchPro 5.0b and beyond should be able to relicense the 6.0 at little or no cost at all. DVDArchPro development is on hiatus.
Holding it hostage by forcing you now to buy VegasPro12 is a grevious insult to the loyal SCS customer base.