This news http://mashable.com/2012/03/11/iphone-ipad-tetherin/ mentions that iTether is an HTML5 app that helps you tether internet to your PC. I dont have an iPhone neither I have used this app. But is HTML5 capable of doing things such as ad hoc wifi hub setup ? I thought these kind of superpowers were available only for native apps.
Perhaps it is merely a web server on their backend and another on your machine to be tethered. Then you just need a small page using HTML5's postMessage to throw things back and forth.
Once you have a channel between their backend and your tethered machine, actually making it useful for doing "real" communications is academic.
Once you have a channel between their backend and your tethered machine, actually making it useful for doing "real" communications is academic.