I was already under the impression that Friends was more popular than Seinfeld especially as here in the UK, Friends gets more syndication than Seinfeld. Friends airs over here everyday and has been airing over here everyday for like the last 10 something years. I think I've seen every episode of Friends on TV a thousand times already and yet I own it on DVD, lol. Seinfeld doesn't get reruns everyday though. Even The Fresh Prince Of Bel Air gets more syndication here than Seinfeld.
I don't think Seinfeld will lose popularity though, it's a sitcom that's timeless like Friends, Fresh Prince etc. It's created some iconic trends and catchphrases. George Constanza is one of the greatest comedy characters ever. Especially with Curb Your Enthusiasm still going and it's connection to Seinfeld, no one is going to forget Seinfeld.