Hazy web graphics

Hello

I recently acquired a MacBook Air - the 2011 13.3" model. In many ways it is a great machine, but one thing I have noticed is that the display seems to be rather poor at displaying small web graphics - for example, avatars on Twitter. These often have a noticeably hazy, slightly out of focus appearance - in contrast to my iMac, where they are pin sharp. Is this simply a matter of screen resolution - obviously I am aware the iMac has a considerably higher res