I've thought about this issue in the past and there are times when I might want to use the small screen and not power up the big screen-
1) to set the PC to record something, say I get up in the morning and remember I wanted to record a certain broadcast, I can do that from the small screen
2) to take a quick look at the weather maybe
Actually I've thought about this with respect to just having a large screen and a small screen beside it, sort of the next step beyond "picture in picture". So maybe the touch screen aspect isn't useful but the screen itself might be useful, and if a person didn't want to use the touchscreen in the front of the case, they could use a small monitor or tv setting with the equipment. Some people might want the HTPC to set in the furniture along with the BluRay player and TV tuner, but others might have a more extensive setup with a place to sit and work, video games, multiple screens, etc.