What you have here is one of the reasons that many of us LOVE Stardock.
Brad the HMFIC there has had the philosophy that dedicated customer support through continued work on the released software works to everybodys advantage. Other larger companies might work through the softwrae development cycle, including the first Beta version prior to final release of their software, and then might offer a patch or two to fix problems that might have come up after general release, and thats it. Thats the last time the developers work at it. So long goodbye. If you don't like it, buy the next version at full retail in a couple years, if there is a sequel.
Stardock is different. They treat us like adults and co-developers providing input. With every game they release they commit resources to support it in patches for a long period of time after the game's release. They not only fix bugs, that crash the game, or are causing problems, but they take our input and tweak the gameplay, add features, improve the game interface and design and listen to us to allow their game to reach a greater potential. And because they can use the feedback of many enthusiastic gamers, who understand this philosophy, they get useful feedback.
If you download only the released versions of the game through the Stardock interface, you are getting the original retail version plus the official tested update patches. If however, you do like many of us do, and live on the wild side, and enable the pre-release version downloads, you can see the newest tweaks and improvements and improve the gameplay a lot. The tradeoff is that the Beta versions are not fully debugged, and may have occassional problems. If you play the Beta and it crashes, you can post the Debugg.err file and provide some insight into the problems so that the guys at Stardock can fix it.
Unlike most game companies, the guys working on Galciv2 update the game constantly, tell us what they are doing and provide us access to these Betas.
So the reason one is playing the Beta versions is that it is the latest version of the game, (a bit unstable maybe) but with the latest and greatest gameplay and interface improvements. And by playing it you can help kill the bugs and provide feedback.
By the Way "HMFIC" is Head Motherf**ker in Charge"

Frogboy rocks !