I agree, Kathy. The show itself was a romance between two characters who met, fell in love, and married. That was the core of the series, so any stories based on L&C would naturally deal with the central point of the series. As you pointed out, the established canon of the series plainly sets up L&C as soulmates, loving each other in any lifetime. Not only that, but the A-plot part of the series only existed to give a reason for L&C's relationship to develop, so the A-plots were never the central point of the show.
In other shows, such as Star Wars or Star Trek, there is no happy romance at the center of the action. A romance may have been on the periphery, not at the center, which was occupied by other things--exploration of the galaxy, the fight against the Empire, etc. So, many other stories with other focuses are possible in those fandoms that can still deal with the core of the show.
Anyway, that's why I think stories in FoLCdom are expected to be romances that end happily. That was, after all, the point of the series.
