Sort of? The thing to realize is that your average speaker leans heavily into the "no true scotsman" fallacy in order to make sense of the world quickly, and so they heavily bias that random distribution from which they are selecting candidates. While I wouldn't personally say "all" in this exact case, it certainly does feel to me as if there isn't anyone new for Twitter to really target, as you have to first discount most of the old people, "all" ;P of the young people, and a depressing number of people who really don't have the resources--time or money--to buy into technological society. Do you seriously believe there is some useful untapped market of people using other social networks--or are even in the target market for a social network but who somehow haven't started using one yet--who aren't using Twitter? I hate Twitter--I'd dare say it is by far my least favorite major social network by far--and even I use the damned thing :(.
