I have noticed this since day 1, IMDB is one of the worst but I also see this on facebook app or the peoplehub. some sites seem to be a lot worse than others but when you see it it is very annoying.
For me any sites/places, which use avatar pictures are blurried. not any other pictures.
Even my photo gets blurried by 920, but it has nothing in common with IE in my opinion.
WP8 might just do some "optimization" leading to lower bandwidth usage, and blurry pictures in peoples hub (including yours!).