For a lot of users on the D1 this is a pretty good upgrade because of LTE. Otherwise, yeah, I don't see how it's that superior to the DX. But if I was upgrading now, it would be the TB.
I have some concerns that they will eventually cap LTE, and since it's different than 3G I have my reservations that you can just pick-up an LTE phone retail or off EBAY and switch to unlimited LTE without changing your contract. Realistically though I do not see changes to unlimited LTE until some time next year when availability is more widespread.
I think a big part is, aside from the Droid Pro and Droid 2 Global released in November, which weren't big hits here, nothing exciting has come out since Jul/Aug or so with the D2, DX and DInc a few months even before that. For all the complaining about too many phones coming out, people don't even have the patience to wait half a year for the phone they really want.