I suspect it was random chance -- your supermarket must have had a run on L'eggs.
(*ducks*)
Apparently L'eggs is alive and well;
http://www.leggs.com/ gives a list of chains and web sites that carry them.
Could be related to the economic problems. I know my supermarket is occasionally out of all sorts of things that you'd expect to be staples. For example, they've been out of skim milk for two weekends in a row, for Heaven's sake! I don't know whether my local market carries L'eggs, but they do have an extensive pantyhose/stocking aisle. Alas, I'm closeted, so I don't buy pantyhose in my local supermarket, or even stop to check out their displays. I just push my cart past them. Slowly!
I think you're right about women not wearing pantyhose as often as they used to. But let's face it, pantyhose are a drag to deal with (sorry!), particularly in the rest room. And it's kind of silly to wear them under slacks, and downright insane to wear them under jeans. Knee-highs or thigh-highs are so much easier. They're just not as much fun. Sigh!
Incidentally, I grew up in the days
before pantyhose, when girls wore stockings and garterbelts (or girdles). Pantyhose became popular about the same time as miniskirts, for some reason.