I'm not agreeing with it mind you, but it happens alot and isn't going to change, so I don't harp on it anymore. Common names are rather useless anyway, if I order something I do so with the full scientific name. Prevents the confusion.
But in the case with both the suams and the mayans, people at first DID think they were riv's and festae, which is why they got saddled with the same common name. But even though we know the differance, since the commons names have been with them for so long, you still see people using them.
But that happens with scientific names too, a lot of people still call port cichlids Aequidens instead of Cichlasoma as an example.