I've only skimmed the arc code, but there is a list of exceptions for domains. The major blogs are on this list.

OK, I checked:

  (= long-domains* '("blogspot" "wordpress" "livejournal" "blogs" "typepad" 
                   "weebly" "blog-city"
                   ; "sampasite"  "multiply" "wetpaint" ; let's just try banning
                   "eurekster" "blogsome" "edogo" "blog" "com"))