This whole "show about nothing" cliche has been lofted as a standard so many times in reference to SEINFELD that I think it is time again to understand the concept.
The "nothing" they refer to is everyday human interaction. Quite simply, nothing is about "nothing," everything is about something (J.P. Sarte notwithstanding). I think the original meaning of this phrase was that SEINFELD did not deal with "standard sitcom plots" that are familiar to us. (In fact, I often think that there is this huge reference tome in Hollywood studios called "The Big Book Of Standard Sitcom Plots" that every writer and writing team refers to.)
I also believe that, before SEINFELD, there was another classic sitcom about "nothing" called THE DICK VAN DYKE SHOW. Think about it: it involved the everyday life of an awkward comic/writer in television with a group of funny friends. Many of the greatest epiodes were about nothing. (I mean, how much more about nothing could a show be than one that revolves entirely around an unwitting revelation that one of the characters wears a toupee...yet it is revered as one of the all-time classic TV comedy episodes from ANY series). The only difference is that it took place in the suburbs and the main character was married (which was the fashion in those days, to quote Grandpa Simpson).