HTC's blog has confirmed that the Android 4.0 updated for the HTC Desire HD, released in October 2010 is cancelled. Android 4.0 was released twelve months after the HTC Desire HD was launched so following the eighteen month support policy that Google is trying to enforce on its OEM partners, the HTC Desire HD should have gotten an update to ICS.
While HTC says that ICS will not provide customers with the "best experience", this claim is obviously bogus. HTC has Ice Cream Sandwich installed on phones with less powerful hardware than the HTC Desire HD, like the HTC One V and the HTC Desire C.
Strangely enough, HTC did not cancel Ice Cream Sandwich for the Desire S and Incredible S, which run on the same processor and chipset and RAM and storage as the HTC Desire HD. So if performance was the reason, well ICS should have been canned on these two devices too.
It really looks like HTC is trying to save a few bucks and time in terms of releasing an Ice Cream Sandwich updated for the HTC Desire HD.
So what is a buyer to do? If updated are a big issue, I would not recommend that you jump over to the Samsung. The did not update their Galaxy S to Ice Cream Sandwich, even though it is essentially the same as the Google Nexus S (built by Samsung) which was updated to Ice Cream Sandwich and is now getting Jelly Bean (Android 4.1).
Sony has plenty of 2011 phones that have less RAM than the HTC Desire HD, but run on the same processor and chipset which it has upgraded to Ice Cream Sandwich. If Sony could update it Xperia Mini's and Like with Walkman to Ice Cream Sandwich, there is no reason why HTC could not do the same for their Desire S, for that matter, Samsung for their Galaxy S.
Best advice? For Android phones buy Nexus phones or buy a Sony.