Why does allmost all LCD HDTV 720p have 1366x768 pixels?

With 720p being 1280x720 pixels, why does almost all 720p native HD TVs have a resolution of 1366x768 pixels, wouldn't this result in interpolation/rescaling if I hook up an XBOX 360 or PS3 and run games in 720p mode resulting in lower image quality? How does this work? Or does the XBOX 360 / PS3 deliver 1366x768 if this is the resolution of the monitor? I'm sure there is something I'm missing here, please someone explain it to me! 8O

Because most computers output 1024 x 768 monitor resolution, so I would assume these LCD televisions LCD panels are built in the same factory as the LCD PC monitors panels...so basically cost cutting.

PS+ I've also heard you can "underscan" some TV's to output 720p, losing a few vertical lines of resolution but also preventing more scaling.