In an effort to address some recent questions regarding the Vita port of the game, the community managers at the Dungeon Defenders team have erected a forum post to help shed some light on important DD happenings. A number of recent developments have been detailed; most notably the complete abandonment of the Vita version. The team explains how they originally displayed a demo of the Vita port last year, and fans immediately noticed it's absence at E3.
No real reason for the shelving is given, other than that they are diverting resources to "other pursuits" (a sequel, expansion or a new IP, perhaps?). My honest guess is that they figured the Vita version just plain wouldn't be profitable, which is not good news for the fate of future indie Vita titles.
In the thread, there's also a number of details given about the console versions of the game, community events, and even a little interview with the map creator. If you're a fan, definitely give it a read.
DunDef Digest 6/13/12 Discussion Thread [Dungeon Defenders forums]