I think if you look at original Raveloft though, you get what a generic adventure is. The characters get swept away from their home, regardless of where that is, and land in a fog filled village with an adventure to complete and a villain to defeat.
The location of the adventure is highly detailed, but its specifically distinct from the rest of the game universe, which allows it to fit into any campaign.
Similarly, you could easily drop Alien into either the third imperium, or 2300 AD, or any other universe, and it would make perfect sense - it doesnt rely on the universe for its effectiveness.
Adventures which are highly detailed, but which can fit into any campaign without needing to say 'oh, if youve already ran pirates of drinax, then.. youll need to modify all these things because this is set in the trojan reach and assumes that a different group was hired to be pirates' are very helpful.