Where you draw the line with superfamily, family, subfamily, genus &c. is determined by agreed convention, not by nature herself. Not all authors appear to agree with the same conventions, though! For this site, Pete (humbly) follows Fauna Europaea and this currently regards the Satyrinae as a subfamily of Nymphalidae. The pertinent bit of the classification can be found on this page of FE:
http://www.faunaeur.org/full_results.php?id=7202
Whatever names you use, it is clear that 'nymphalids' and 'satyrids' are more closely related to each other than they are to, say blues (closeness of relationship being determined by how far you have to go back to find the most recent common ancestor of all in the group). It is also clear, as you point out, Annie and others, that the marbled white is a satyrid (whether that means subfamily Satyrinae or family Satyridae).
Guy