They are using some form of AJAX (JavaScript talking directly to their server without reloading the page).

In this case they appear to be using PubNub. http://www.pubnub.com/how-it-works

They're constantly requesting a JSON file about once a second. Example contents, formatted: http://pastebin.com/uMv7d8xS

Seems like excessive transfers. I achieved a "real time" counter by having requests return a start value and a rate of change per second. The GUI would then update every second with the estimated values. My AJAX requests would happen much less often and update the start and rate of change.