It says “Wide @font-face support means Font Awesome even works in IE4” but not as the way it is implemented on the demo page.
That technique is not compatible with browsers that do not support the :before pseudo-class (eg. IE7). The icons could be used though, but not that way.
That's a great point, as far as the the LESS and CSS go, which were optimized for Twitter Bootstrap. If you're not using that TWBS, Font Awesome would just take a bit more work with CSS. That's a great idea for a fork.
That technique is not compatible with browsers that do not support the :before pseudo-class (eg. IE7). The icons could be used though, but not that way.