"The sole reason most likely being Ubi Softs intention of supporting their Ubi.com player matching service."Not sole reason, as is stated, many reasons.
"I was of the impression that since the game is built on the Unreal engine that it would naturally have support for the Zone since it has dedicated servers and web based methods to join a server."
Nope, the Zone doesn't have technology allowing support of a wide range of games using the standard setup e.g. master server with server log of all servers hosted, like programs in-game browsers , Gamespy 3D, Gamespy Arcade (for some games, Rogue Spear uses its anounce tech) and All Seeing Eye use. It doesn't have gamespy's tech that allows modules to be created very quickly and "plugged" into gamespy arcade. If it has to be supported, Zone has to make a new client, obviously using there basic template, and Ubi has to support Zone (though the Unreal Engine does have features already in place). Ubi.com will most likely have to be redesigned around Raven Shield like Zone will be.
"If anything, it would seem like they would have to go out of their way to make it not able to work on the Zone which is hardly a technical reason."
Read above, and Zone charges for use of its servers. Though gamespy does charge for Master Server file services, Ubi is using its own server. Gamespy is free for the service Zone offers. Ubi.com will be *free* too, but obviously Ubi.com has to be paid for.
