For additional context, the commercials started off as a regular TV spot, but then they expanded them a bit a few years later.
Original commercial, I think:
https://youtu.be/H9nzGTo_SyQ
Follow-ups:
https://youtu.be/Ao-Lj2x-yRE
https://youtu.be/dsNsWv3TapA
Also, Seinfeld placed various Superman references in the show. The best such reference was probably the entire Bizarro episode.