I'm not even sure it improves touchscreen UX. Most touchscreen devices also have small screens, and I really hate viewing a mobile site that's 50% whitespace. If my screen is only 2x5 inches, I don't want any of it wasted with useless whitespace forcing me to zoom in to see anything. At this point, I'm starting to suspect that most designers actually don't have any clue what they are doing and the entire discipline is 90% following the latest trends.