I don't have any proof to back this up but I am pretty sure that a firmware and software update will be two different things. In fact, HTC may be the one to issue the firmware upgrade from their site. Samsung did it with their Omnia. I also don't believe that a firmware update is going to be released OTA because, unless Android does something much different from others, a firmware upgrade will wipe out your entire phone and put 2.0/2.1 in 1.5's place. In cases of most other firmware upgrades on phones and other devices, this means that if your phone happens to turn off during the upgrade, you will have a paperweight in your hand. That is why Verizon has required that you bring in your phone to have most firmware updates done in the past. I was very surprised that Verizon allowed Samsung to release their update over the net and they paid for it because a lot of people who didn't know what they were doing bricked their Omnias.
SO....unless Android has significantly changed the game, I would expect there to be a download from the net with OS 2.0/2.1 along with a program that automatically does the upgrade for you. The upgrade over internet ensures that your phone is plugged in for power and warns you 50 times that if you turn it off, unplug it, or have your battery go dead, you have a paperweight. OR, Verizon will simply require you to bring the phone in.
Edit: Just thought of something. IF this update is about to be released, it must be a tide-over for a date that's further down the road for 2.0/2.1. This update would be useless for 2.0/2.1 so why go through the trouble to make it if you know a major firmware upgrade is being dropped at the same time or even within days?
