Well, the reason why I'm asking that question is because pretty much every game with high sexual content or almost near high is frequently being associated with nukige by readers. "Tick Tack has a dozen h-scenes it almost feels like a nukige" is the best example for dumb statement. Its kind of a misconception. While it is true that most nukige has a lot of h-scenes, that is not the primary requirement. If you think Koihime Musou is the latter, i.e. subplot event is an excuse for h-scenes, then I think it is fine to consider the events as nukige, though it is stretching it a bit.
Nukige is best described as "porn without plot". Even if it has a story, both main plot and subplot is made solely for the purpose of showing h-scenes everywhere, heroines is created only to be fucked silly and doesn't develop beyond that (people can't even remember a nukige heroine name most of the times, can they?), and scenario is written only for sex purpose. That's a nukige imo. Sometimes, even if you might find a resemblances of an actual plot in a nukige, it is very very minor.