I suspect people using a Retina display are more than likely to be using a WebKit browser, so it's easy to make icons render nicely with just the font technique

I suspect people using a Retina display are more than likely to be using a WebKit browser, so it's easy to make icons render nicely with just the font technique. This is my motivation for wanting to use a font for icons. But to improve the quality on the desktop in other browsers, you can use a canvas element. And you don't lose anything over image icons when zooming.