I preordered my D7100 from Bel-Air Camera in Los Angeles, CA and at the time I ordered it, they said they were expecting it earlier than March 21, though they didn't say why. Now, NikonRumors noted that Amazon has moved up the D7100 ship date from March 21 to March 14, giving credence to what the Bel-Air Camera folks said. I will double-check with Bel-Air on Monday.
If you are interested in the D7100, join the D7100 Flickr group. I will be posting there regularly.