Has the X-Men replaced the JSA as the team of choice? When comic fandom first really started in the early to mid 1960s, we had the FF with less than 100 issues out, the X-men who would go into reprints soon, and the JLA (Sekowsky, ewww) which was an extension of the JSA. I believe that Roy Thomas, an important and early fan, was a big promoter of the JSA.
Skip forward 20 years to the 1980s and we have Byrne/Claremont doing great work on the X-men, FF is getting tired, and the JLA is near-extinct. New fans are going to go for the X-men as the team book of choice. I think that momentum has held out over the decades. New GA fans, who weaned their super-team teeth on the X books aren't likely to go back to JSA. They're likely to go to DC's big three, TImelys, or to veer off into other non-hero GA stuff.
My speculative on the whole thing.