SlashGear has confirmed with HTC today that the Desire HD, Desire Z, and Incredible S (along with the standard Desire) will be receiving the bump to Gingerbread some time in the second quarter of this year. But, there's a potential caveat: US phones might not be included.
It remains unknown if HTC was also referring to carrier-branded versions of the aforementioned devices in its statement, and if it was, if those devices would be receiving updates at the same time as their unlocked, HTC-branded siblings. Phones in this category include the HTC Thunderbolt and Inspire 4G (both based on the Desire HD), as well as T-Mobile's G2, the EVO Shift 4G, and possibly the HTC Merge (all based on the Desire Z).
Why wouldn't they receive updates at the same time? The US, carrier-branded versions of these phones all have minor hardware differences compared to their European next-of-kin. The Thunderbolt has a front-facing camera and LTE, while the Inspire 4G has HSPA+ and a noise-cancelling microphone. These are the kind of minute hardware differences that necessitate different ROM builds based on region, as well as different radio firmware. The Desire Z variants all have slightly different keyboards, and completely different cell antennas.
It'd be nice if HTC's statement encompassed all of the many American iterations of those handsets, but I can't say I'm holding my breath.