Smartphones and tablet gaming got popular because they are available almost to everyone. Anyone , even people who don't play games that much, can buy them , and they have available digital stores with games. People buy them mainly for another purposes.
I don't say here ,necessarily, that you can't be interested in gaming on them if you mainly game on a console or a PC, but I think that type of gaming won't grow that much, because most of people who game on smartphones or tablets have that "interest" for these games and they don't really like them.
Besides , even with later installment of smartphones like Samsung Galaxy S3 , gaming on it with just touch screen feels so awkward and unresponsive, so even if want to play some real portable games, I would go with something like the PSVita over any smartphone or tablet.