Because the quicker its dropped, it will become the standard for all dev's making up new roms
choices, options, etc.
Since HTC hasn't made an official statement on this yet, the only thing we can do is to track their movement, so to speak.
1. HTC's process it to first adapt Sense to an Android OS, then port that OS to a platform, and then to further port that platform version to each phone/carrier. An example would be when they ported Sense to Android 2.2, then to the Desire (which is a platform), and then to the derivatives (Evo first, then Incredible). The Desire got it August 1st, the Evo on the 3rd, and the Incredible started its roll-out on or around the 26th.
2. "New" Sense has been ported to Android 2.2.1. The Thunderbolt will launch with this. The Desire HD and Z have this. HTC's Spanish Twitter stated that all current 2.2-based phones will get it. So once again, we can expect the unlocked Desire to get it, followed by the Evo and Incredible.
3. So far, HTC has NOT finished porting Sense to 2.3. This is evident in that the Thunderbolt was demoed running 2.2.1 and will launch (presumably no later than March 1st) with 2.2.1. The Thunderbolt is on the Desire HD platform, so when we see the Desire HD's update announced, we can speculate that the Thunderbolt's isn't far behind.
4. The Desire's successor is supposedly going to be announced at MWC (February 14-17 this year). If that does occur, then it's safe to assume that the original Desire will soon hit EOL, and thus, not see updates after 2.2.1. If this does occur, then a 2.3 update for the Incredible is pretty much dead.
So my speculation based on the above is that the Incredible will get 2.2.1 + New Sense, but not an official port of 2.3.