Blog that are likely to drive sales tend not to be very typically blog-like. Dave Beckerman may be the sole exception, simply because he
is the exception.
Noah Gray's multiple blogs are another example that
might drive photo sales but really they promote his blog software (GrayMatter) more than sell prints (I prefer Moveable Type, personally).
I've been astounded to sometimes see my blog get as many as 1000 different visitors a day (usually around 3-400 though, not counting web spiders). In all those browsers, only a handful even bother to post a comment, much less buy anything. Heck they won't even add me as a
photoblogs.org favorite 
ingrates