Not all HD TVs are the same. You have standard HD TVs and now you can have the higher specification of 1080p HDTV. 1080p means you have full 1920x1080 pixels on screen instead of 1368x720 resolution on normal HD TV. That is 110% more detail than before.
1080p allow you to enjoy the full picture detail on the latest HD DVD, Blu-Ray and the latest games consoles such as the XBOX 360 and Sony PS3 which all runs best on 1080p.