As to why GameTap has yet to release the game, Marchini -- himself a "self-confessed Sega fanboy" -- told Joystiq, "The main factor keeping GameTap from releasing PDS [is the] complexity of Saturn emulation." (We believe him, the Saturn was notoriously difficult to program for.) He notes that it can take months to properly prepare a single title for release "or worse, to discover that after months of development the game will not be releasable." He adds that it's a matter of the amount of resources needed to release a game versus its worth to GameTap. Naturally, the larger a game's potential audience, the more beneficial it is to GameTap.
Thus, it comes down to consumer demand, and that's where you come in. Marchini informed Joystiq that GameTap has set up a poll about Panzer Dragoon Saga on the GameTap blog and said that the company will be keeping an eye on Joystiq's poll as well (be sure to cast your vote below). "If the audience is large enough to justify development time," said Marchini, "GameTap would reconsider the PDS as a higher priority."
You heard the man, get to it!