I think the combination of people having more disposable income that grew up with pinball, coupled with the need for having something unique that they can call "their own" has led to the boom. Pinball helps to give people that feeling of having a unique identity and an individualized experience. It isn't a $2 app you can put on your iPhone to be just like everyone else. Nor is it formulaic in that you just keep pressing the same 2 or 3 button combo to master the game. People are burnt out on cookie cutter games and looking for something new and that presents an individual experience - and pinball brings that to them. Just my 2 cents