I agree their demographics were interesting, but I think that's more indicative of the "casual games" space in general, not specifically something Zynga uncovered. For example, PopCap Games had a big hit in the early 2000s with Bejeweled, which had a similar demographic profile.
And, while they didn't make any money on their own, there were some '90s games like that as well. In his book on casual games (http://www.amazon.com/gp/product/0262517396/ref=as_li_ss_tl?...), Jesper Juul also notes the interesting existence of very hardcore Freecell and Minesweeper players, who tend to come from nontraditional gamer demographics and don't consider themselves "gamers", despite objectively playing many hours/day and becoming very skilled at their games of choice.
And, while they didn't make any money on their own, there were some '90s games like that as well. In his book on casual games (http://www.amazon.com/gp/product/0262517396/ref=as_li_ss_tl?...), Jesper Juul also notes the interesting existence of very hardcore Freecell and Minesweeper players, who tend to come from nontraditional gamer demographics and don't consider themselves "gamers", despite objectively playing many hours/day and becoming very skilled at their games of choice.