Well, I'd say most reference Reeves and Kidder for a couple of reasons.
First, the 50's TV series doesn't re-run as much as it did for many of us when we were younger.
Second, and more to the point, Bryan Singer and the writers of RETURNS make it a point to reference the '78 film version (and to a lesser extent, SUPERMAN II). The Music, the outtakes of Brando and even some of the plot threads and in-joke references. Many, in fact, have referred to this as SUPERMAN 2 1/2 (ignoring the original series' III and IV).
As I noted, by explicitly calling attention to the earlier films, it presents SUPERMAN RETURNS with some conundrums because Routh and Bosworth simply play younger than Reeve and Kidder and this film supposedly takes place sometime between 5 and 8 years AFTER SUPERMAN II (And by then, Kidder was 32 years old. Which means, in effect Bosworth is a 23 year old playing someone who conceivably be 37 years old). It's not a big big deal to me (and neither are the costume changes per se), but Singer and his team have brought this on themselves.
As I noted, I think it would be a great declaration of independence (
) if they dropped ALL references to the earlier movies for SUPERMAN RETURNS PART DEUX.
).