The HTC DROID DNA was the first device to bring a 5 inch 1080 x 1920 resolution screen to the party. When you talk about resolution, the 441ppi was the at the top of the industry at that time. The phone was available inside Verizon stores starting November 21st and it is believed that Verizon didn't want to waste all of the marketing dollars it had spent on the phone, so it held back from committing to the HTC One, especially since the latter has a smaller 4.7 inch screen. But because the resolution remains FHD, the HTC One has an industry leading pixel density of 468ppi.
Verizon had a promotion recently that offered the HTC DROID DNA for free with a signed two-year pact. That might have cleared the shelves in time for Verizon to start selling the HTC One on August 15th as the latest speculation suggests.
Thanks, Anonymous Tipster!