Maybe nobody explicitly suggested otherwise, but I just wanted to highlight that time is a human concept and in informal context can mean a lot of different kinds of things (e.g. a time of recurring event). When you start formally modeling those, a single timestamp isn't enough.

Actually, UTC isn't enough for storing a date, at least not a date in the future. If I schedule a single event for 3pm on October 1 (currently in the future), I expect it to stay at 3pm. Even if my city hosts the Olympics: http://support.microsoft.com/kb/257178

Note also that not all governments are in the habit of giving sufficiently advance notice of daylight saving changes.