Here is some more evidence that Samsung likely duped T-Mobile into believing there would be a 2.x update for the Behold II (which is probably why some of the Reps at the stores led their customers to believe an upgrade was coming), then Samsung later changed their mind for whatever reason:
At 32:33 into the Thursday (5/20/10) podcast
on AndroidGuys, you clearly hear the TMo guy, Kevon, mention that Samsung representatives visited T-Mobile and asserted that they would have 2.1 for the Behold II. HOWEVER....he then goes on to mention that this event was several (6!??) months ago.