From twitter with HTC officially chiming in at the end:
@
Social_Selleck I think its dictated by HTC. My personal opinion.. They are the ones that approve and release the updates to their phones.
Social_Selleck wrote "@
jjolc Yes, and @
htc has been working on the update since Google provided the source code. Google dictates updates."
@HTC writes "@
Social_Selleck Fair point. The carriers have a big say in updates as well
"