I want to clarify this - you can only play the game in conjunction with Internet? That is, there are NO offline playable modes on it (only available as a game DOWNLOAD, not game disc)
MMOs have new content and fixes added at a rapid pace. There's often something new added every month, sometimes even every week. So it doesn't make much sense to put it in a disc as that disc would be outdated in a week!
Neverwinter, another Cryptic MMO that was ported to XBox last year, didn't seem to have very many issues when it launched. The same team that was involved there are helping the STO team. So, the issues should be minimized.