It's odd that no one has mentioned this, but part of the reason no American thought they looked like "Y-fronts" is because American briefs don't have a Y-front. I have never seen underwear that looks like the first and third example on the rjmetrics site. If you do a comparative images search for "briefs" and "y-front" I think it'll be pretty obvious.
Jockey (and only Jockey, as far as I know) used to have a Y-front, which is one of the reasons they never sold well in Canada. I still completely ignore the brand even though they changed to a more typical fly a couple of decades ago.
