HTC: Sense vs. Android Stock UI

[jdub01984]

That is only part of the answer to your question. Yes, HTC has to add all of their features to the rom, but more than likely they are doing that with test builds that google is supplying them with, so when the official build is released they only need to make small fixes.

The real problem is the individual carriers have to test the finished upgrades and sign off on them, before they can be released to you. So more than likely if the upgrade is out for some, then it is your carrier taking their sweet time approving the upgrade.