TL;DR: Numerous reasons:<p>1. 1024<i>768 was already the XGA standard, and increasing WXGA to 1366</i>768 was the easiest way to do this and retain the height of 768. If the height changed, other (small) things would have had to be changed.<p>2. The bizarre aspect ratio, 683:384, reduces to 16.008:9, which is very close to the common aspect ratio of 16:9. 1365.33<i>768 would give 16:9 and a fractional pixel.<p>3. The resolution of 1360</i>768 is uncommon, but video data can be stored entirely in an 8MiB memory chip. Adding the extra 6 lines requires a slightly more expensive 16MiB chip. Not sure why they didn't go with 1360*768.