Yeah, to really be accurate it should probably be tested with a blog and a content site, internal and external links, and there should probably be a minimum of 4 test links on the pages used for testing. One in the bread crumbs, one in the main nav, one in the text (content area) and one in the footer with the nofollow rotated through them, and on the blog another link in the comment section should probably be added... This is one of the reasons I didn't bother before, and I think they could certainly be treated differently between internal and external. It makes the most sense (in a nonsensical way or course) to apply nofollow one = nofollow all on the external links on a page, but not to the internal links on a page.
So I could fairly easily see the following being applied, whether it makes complete sense or not:
nofollow on one external link on a page = don't credit any links to the external page
nofollow on an internal link = pass the PR anyway as long as there is one link
Even reversing it on internal links, and disregard the nofollow all together and if there is one follow link to the page, treat all the links as live and score / credit the text the same way, because the only reason I could see to nofollow one internal link and not another is sculpting, unless your blog comment idea is used by someone, and then it's still 'the right thing' to go ahead and count them all... Why else (besides sculpting link text or PR) would someone nofollow one internal link and not all of them? An accident? Count 'em all sounds right... On purpose? You're trying to game, count 'em all... Someone else did it? Count 'em all...
Of course, if you wanted to apply an indirect filter or penalty to the sites trying to sculpt with nofollow I couldn't think of a much easier way than to let them decimate their PR flow by applying nofollow one = nofollow all even on the internal links on the page...
But, there's quite a bit more testing than I care to do to find the answer to a question I don't really care what the answer is to, so I'm not going to do the extensive testing I would if I really cared, but it makes some sense they would treat internal and external differently, but IMO it's really not worth the risk of having them change their mind and if for some reason I nofollow an internal link on a page I nofollow them all, because then it removes this question from the equation.
There's better ways IMO to get the text I want counted in the right place or keep a page from receiving PR from internal pages than leaving it to a 'Gwhim' that could change at any moment.
[edited by: TheMadScientist at 2:13 am (utc) on Jul 4, 2010]