Most carriers tend to upgrade their newest phones first, as these phones are still "cutting edge" and more importantly, still available for retail sale. These are the phones that the carrier is advertising and selling against the other carriers.
So, you're better off comparing the Incredible's 2.3 update with similar updates for carrier-branded phones of the same generation. So, how does this look?
AT&T: They didn't have a single Android phone out when the Incredible launched, and only had ONE Android "high-end" phone launched in 2010, the Xperia X10. These guys just got Android 2.1 (yes, two point one!) less than 2 months ago!
Sprint:
Their killer phones for 2010 were the Evo 4G (the Incredible's big brother) and Epic 4G. Epic just recently got 2.2, and the Evo has received 2.3.
T-Mobile: Other than the Nexus, I don't know of any 2010 releases getting 2.3 yet, but then, I don't pay much attention to TMO. Fill me in here.
Verizon: The big releases in 2010 were the Incredible, Droid 2, and Droid X. The Droid X got the update and it's been a fiasco. The Droid 2's updated was announced as delayed after that fiasco. The Incredible hasn't gotten it yet.
So, of all of the 2010 "super phones" not named Nexus "Something," only the Evo and Droid X have recieved Gingerbread. Not surprisingly, these were the top 2 selling Android phones for the year in the US (Incredible was 3rd). We'll get ours soon, and my guess all along was in the August/September time frame (so long as you ignore my original guesses of March/April/May/June/July).