Aside from the added screen real estate, I find my external 1080p LG monitor simply looks better than my Dell Latitude's. The laptop display just looks... cheaper. It's hard to explain, it just looks worse.
The whole "HD ready" thing was an utterly sad part of the story of cinema/television that let's hope will never repeat.
As for the 1366x768, for some reason for many, many years the wide majority of monitors stopped there, with "Full HD" coming to the masses (but not all) only a few years ago.
"1366x768" meant "half baked HD" from the day it was introduced, so it's understanding that few quality monitors (and especially laptop screens) were made with that resolution.
