If you are considering to buy a HTC device or already have one then you should definitely visit this website: HTCClassAction.org. IOW a range of HTC devices that have Qualcomm CPU (MSM7200 and MSM7500) lack of proper drivers. I own a TyTN II and I can confirm that UI is really crappy slow while the paper specs looks far better.
Now, why would a manufacturer decide to cripple its devices? My guess: most probably because there are no proper drivers from Qualcomm for Windows Mobile. Yet. So we all have to wait for proper drivers to emerge. And here we get a real problem. HTC is playing dumb, denying the problem and stalling which is a completely wrong attitude from such a company. Instead of saying something like: "Qualcomm screwed us with not providing the drivers, we are pushing them, will update drivers asap (i.e. month/year) and sorry for all the problems" they are playing dumb. "Luckily" the number of angry users is raising, petitions are being signed, news is spreading through online community and lawsuit is being prepared. And perhaps HTC will change the attitude, after all the public image is important and even HTC should understand this.
At the end, even though we might get proper drivers, a black spot will remain on HTC for a long, long time. The fact how they are dealing with the problems might turn away a lot of existing and potential customers. I hope that this will serve them as a lesson where to improve.