Knowing a bit about how Basecamp works after reading all of Jason Fried and DHH's books and blog, I can't really see how there could be a gender gap over there. No one has to negotiate. The salary for a role is dictated by the market average for that role rather than the person doing it. No one has to negotiate a raise. Everyone gets the same raise to keep inline with the Bay Area market rate. Given those two things it'd be very hard to pay one person less than another if they're doing the same job regardless of any demographic differences between them.
Basing the salary on the role rather than person doing it seems like a really good idea to me.
Basing the salary on the role rather than person doing it seems like a really good idea to me.