The span of Simpsons meme literacy is identical to the span of western civilization.

Span? Yes. Density? Not as much. I only say it as I've been surprised on several occasions by American friends living here voicing the same thing. I think it may have been in part due to some fortuitous scheduling making it so that literally every Irish person above a certain age has seen a heap of episodes. That and possibly that there wasn't much else on.