Well no, that is not a yuri specific thing. It's the most common thing in all versions of romance, from het to yuri to yaoi. That's just a popular story structure.
interestingly, my favourite yaoi (actually one of the very few I like), Mainichi Seitan, does a lot of "what happens after they get together. There are three couples during the series that get together at different times, but the ones who were already dealt with are still shown either working through their own relationship issues or simply being together as couples while the next focus is doing their thing.
Come to think of it, Dykes To Watch Out For was/is like that too, where couples get together, spend time as couples, sometimes break up and new couples form, etc. and it continues being interesting. The big cast and ongoing format helps a lot.