The hinting on Typekits version is pretty shitty on Mac …
I think the term you are looking for is “rendering”. The Mac doesn’t use the hinting included in the font files — it comes up with it’s own interpretation of the curves as pixels. From what I can tell it looks like it struggles with the complex g and the light weights. These kind of issue will be there in all fonts.
… and even worse on Windows.
Look at the difference between IE8 and Firefox in Win 7. Something is definitely wrong here. I suspect the browser samples are to blame.
Are you planning on using this for text sizes?