Due to the current demand for the Desire - ie outstripping supply in most cases, I hardly think HTC would even dream of bringing out a succesor, to what is still a very new handset...
Maybe in a year or so, but it would be suicide to do it now - Cancelled orderes and unhappy recent buyers? I think not... And thats before the networks even have their say, and believe me - in todays world, networks can make or break not only a handset, but also a company - Even if they are as big as HTC...
Think about it - The networks go all out to push the desire (Iphone4) and all of a sudden, whilst they stillhave back orders, the manufacturer announces the Desire HD (IPhone5?)
It won't happen...
Mike