@ X-Raider : It is never "silly" to ask a question.
Computer game developers often use the Greek alphabet to label the series (A/B/G) of major phases in the development of computer games :
1. ALPHA builds (letter A)
2. BETA builds (letter B : which include internal betas and public betas)
3. GAMMA pre-gold-master builds (letter G : comes before the D of DELTA, in the Greek language, skipping C)
Not all developers test Gamma builds : often, they go from the most advanced Beta build to the "gold master" that will be used to manufacture the commercial, release version.
I suppose, here, that GPG and SD are currently holding an internal, closed, pre-release phase of testing.
There are some features, such as in the Internet Games lobby, that are being tested during that Gamma, and that we will not have access to before the mid-April release version.
I'm happy with the state of the game at the moment, despite the Spartan lobby, and I look forward to being surprised, in a few weeks, by the new features which they are currently Gamma-testing.
Since I have no inside info whatsoever from anybody at GPG or SD, feel free to correct me if you are one of the cognoscenti.