There's a ocean of difference between the human form and the sails of a ship :)
Man knows man, there's no difficulty there at all. Maybe a few minutes hesitation as you say, but that's all.
I should add that I also heard this story, and even though I have no way of directly confirming it, the academic consensus seems to be that the tribe really did not recognize what the photos depicted. I'm speaking of an "academic consensus" because (a) it was an anthropological study, and its claims can be wrong just like those of any scientific study, and (b) I actually heard this story in an art theory seminar, so that should count for something.
Sure, it sounds hard to believe for people like us, since photos are so seamlessly integrated into our daily lives. But let's assume for a moment that this story is true - it wouldn't be too hard to explain, I think. When it comes to photos, shape is reducible to contrast. And while contrast does play a role in recognizing real people (and as such, contrast must play a culturally independent role in visual identification), it's hardly the decisive criterion. In fact, there is still much debate about how visual identification works. One of the earliest psychological theories claimed that visual identification of objects depended crucially on the mental matching of perceived and remembered shapes ("Gestaltpsychologie" ). If I remember correctly, this theory ran into problems because it had to assume an infinite mental storage, since everyone one of us would have to remember every possible shape of an object in three dimensions. Current neuro-sciences put much more emphasis on movement (when it comes to biological objects such as humans and animals) and functionality (when it comes to inanimate objects - canonical neurons, of which the famous mirror neurons are a sub-species, are relevant for recognizing functionality). Since photos do not show movement, this would be a neat explanation, I think!
Sorry for digressing, I just thought this might clear up some loose ends.
As for the main topic, some stories are about sex, so they should involve it. But they don't have to be sexy in any way...
As for what sells better, I think it's "sexy". Sex is too much of a taboo in any society to really sell products which don't deliver real sex (by that I mean to exclude the porn industry, which obviously sells a lot more than Hollywood does! But to me it seems like they sell sex itself, if only masturbation...). But if you want to sell a tooth-brush (or, more likely, a comic which is not primarily a porn-comic), I think going with sexy would be the better choice because it can actually become part of socially acceptable everyday life :P