The dances move up the social scale as the opera goes on - first the peasants at the end of the harvest, then the country-dance for the gentry at Madame Larina's, then the grand ball in St Petersburg. Only the last feels a bit like a divertissement to me (especially if they repeat the schottische).

I meant to say that another tricky thing is that hardly any of the Tatyanas that I've seen or heard have been able to encompass both the romantic young girl and the older and wiser Princess - most could do one but weren't so convincing as the other.