you know, that is very strange -- I checked one version of apache, and the :80 doesn't work, another version and it does. I don't really see any changes to the mod_rewrite code between them, but, the request processor seems to change what it sends based on the way the header is received.
It is interesting, I guess the :80 is required based on how the request is sent through.
From the testing I have done, those (www\.) matches are slower than two anchored matches, however some floating matches, like
RewriteCond %{HTTP_REFERER} mokkels.nl [NC,OR]
can actually be faster. Because it is not anchored and there are no metas, most regexp libraries translate it to strstr
I'm also not a fan of the /.*$ at the end
For some reason, those appear to evaluate slower.