There is no need for JS on a site like this. The ajax upvote is convenient but they could (unconveniently) reload the whole page and set the location with an anchor to go back to the upvoted comment, 1994 style. Any real time notification system requires a backend infrastructure that maybe they don't want to have.

They could also use a better CSS but who cares, text is king in this kind of sites. It displays quite well on mobile too, especially with Opera which reflows text after zoom (the very reason for using Opera).