I think we've had CMs say that the circle section of the DL scanner is empty, but I still find it hard to believe that the WDW and DL scanners are drastically different from a hardware standpoint. The light-up section seems to be identical. From my own (quick) glances at both in person, it often felt like the DL scanner simply has a plate over where the RFID scanner would be - you can kinda see it in the pics. (It's gently thicker inside the circle.)
While I doubt they've done the conversion yet, too - it wouldn't be out of the question that they might do the upgrade covertly.
(I keep meaning to tap a WDW card against that section at DL and see what happens, but I never remember when I'm there.)
I'm betting there's a supply or tech issue with MB+. I mean, WDW accidentally sold a batch of them two months ago, so they definitely have stock of some kind. I can't imagine that anything would happen at DL until long after WDW's full release.