Exactly. If I run an XL game, I expect you use XL. If I run a Rebirth game, I expect you use Rebirth, standard Descent DOS versions, D2_3DFX, or Descent II Win95. The Rebirth development team's primary objective is to maintain full compatibility with the other versions. That is why Kali uses it (because other pilots may still prefer the older versions). It is updated extremely infrequently, but this doesn't matter -- it doesn't have to be updated much at all. Its intent is to "remain oldschool" while running in hi-res 3D accelerated modes. Since XL does not share this philosophy, Rebirth and XL games tend to be separated, to minimize any chance that there will be a conflict between the two. Small Descent competitions and ladders still exist, and thus, standardization of player clients is a precautionary measure.