My understanding is that this sort of thing is pretty common. Traditionally, "rape" required the victim to resist "to the utmost." Our idea of what constitutes rape has broadened considerably, but the law is sometimes slow to catch up. According to this, five US states still have such requirements in their laws:

http://www.womenslawproject.org/resources/Rape%20and%20Sexua...

Many others make no mention either way, and I suspect many of them would then fall back to the traditional requirement.