Simple: there are fewer synchronous/blocking steps involved. The server can get the data, render the HTML, and stream that right to the browser. The user has the content the instant that the response is received, while a client-side approach would have to wait for the JS to load (even if it's in the cache), interpret, then execute the "onload" code which then renders HTML via some template, plus any time to fetch extra data needed over the wire. As a case study, take a look at GitHub's source - the time to render the page is typically in the 100ms range, and it takes another ~2s or so for the page to fully initialize (according to Firebug). If GitHub decided to render everything on the client, I can pretty much guarantee that it would not appear as snappy.

On a side note, it almost seems like you're trolling - given that your own site seems to render content on the server. ;)