The US is bigger, and has more first-rank universities, than the UK. So on the plausible hypothesis that the number of people who can be rightly called prominent in a given large community is roughly independent of the size of the community (since I'd expect it to be a matter of how many people one can remember easily) the threshold for prominence in the US should be higher.
(I take it that "prominent" here means something like "with a reasonable chance of being one person a crackpot picks on when s/he goes looking for an academic in the relevant field to contact about his/her crazy theories". I don't think this implies "well known to the general public", though doubtless professors who are well known to the general public get more crank mail.)
I think that it should be strong evidence for ‘better known to the general public than most’, but not strictly implying that, nor good evidence for ‘well known in an absolute sense’ (although that depends on where you draw the line).
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: