It just isn't their thing..I think. They are busy with updates that everyone is moaning for and I imagine the lost time in dealing with T-shirts just makes no economic sense. BUT, I think they could easily out-source this to someone who IS in the business.
Last Christmas I suggested that they should sell T-shitrs, mouse pads, etc for us to buy (or more accurately have-bought for) through the HTC site.
I also suggested a button on the web-site that would enable you to sign up someone as a gift and have HTC send an e-mail to the individual on the 25th evidencing the gift. Could be automated so that no-one actually has to send any mail on that day and a form letter could be used for notification.
BUT...no one listened. *sniff*