You could write a simple greasemonkey/userscript type extension to hide those (a custom css might be enough as well with a style override extension). They shoudl build it in though.
I've done it before for sites where I needed to do repeat operations many times. Remember early on someone made one that added some extra features to memo (block & neverending feed).
If you can get this style:
div[id^="show-muted-"] { display:none; }
into your browser's user.css and it supports CSS3, they'll be hidden.
