The border is an insignificant portion of the screen unless you are loading the site in a small window or very low resolution (such as 640x480). KISS is actually not taking over for web sites, as they are already generally designed really simplistically (and have been for ever). There is nothing to take over.
Also, with the broadband resolution, more and more people are getting on fast internet connections and the extra load time is not that significant for them.
Also, the border only loads once when you first go to the site. If you stick around and spend more than ten seconds looking at it, that extra load time in the beginning is quite insignificant. Do you complain about the extra time you have to wait when starting up a computer game? I would certainly hope not.