there's one major flaw in your observation; google worked exclusively with motorola (first) and HTC (second) to design a google experience phone. all other devices that have come out since, haven't had the same level of interaction from Google.
Google announced before the I/O that the newest update will be concentrated to DROID/N1 first. these are both Google's flagship "experience" devices, regardless of carrier.
Try looking at the picture from a global scale. Which of those newer CDMA handsets are available in any other country other than the US? The EVO/Incredible are N1 replacements. HTC most likely brokered soem sort of deal through exclusive licensing with each carrier in order to sell these products. It's something they're very well known for.
In my mind, the most likely scenario will be, HTC will get the update for the N1 and then retrofit it to work with the EVO/Incredible so as not to eliminate the Sense UI from the mix.
I don't know where this discussion of older handsets came into play, but this is technology. Manufacturers have NO obligation to provide latest software to these devices. The only thing they could be possibly be held accountable for are security updates. If you have a pre-DROID phone, you might as well start phone shopping.
I think we may be talking past one another. My focus was not on which manufacturer receives the 2.2 update from Google first. In fact, I assume they will all receive it simultaneously through the quasi-independent Android organization.
Rather, I was speculating (and it's pure speculation) on when the various carriers would receive the updates from the manufacturers and when they would release those updates to their subscribers. It's this last stage that matters to consumers.
I think there's no doubt that the N1 and the Droid are the "easiest" targets for updating. Neither has the Sense UI extensions wrapped around the o/s. But I remain skeptical that VZW is going to release a 2.2 update for the Droid ahead of the Incredible even if it's ready before HTC has completed the extensions for "Sense" and passed them on to VZW.
As for older devices, you're absolutely correct that no carrier has an obligation to update them. Sorry if I left the wrong impression. And from a marketing/sales perspective, there's little value in providing such updates. So it's a little surprising (to me) that VZW decided to update the Eris to 2.1 even after discontinuing sales of the phone.
But given VZW's action, I have to wonder what they and other carriers are considering for similar devices. What about the Devour? The Ally? I would have guessed that neither is likely to be updated. But after the VZW update of the Eris to 2.1, you have to wonder if other models are also in the pipeline for updates and whether 2.1 is the end of the line for them or they'll be moved to the 2.2 standard when/if it happens.