Eh. I don't think most people actually buy action / shooter games for the story, so I doubt that's even relevant. Note how all the best selling games have a strong multiplayer focus, which has nothing to do with story. If multiplayer were removed from these games, I guarantee you their sales would plummet.
And keep in mind, not even all single player games are bought for story. I enjoyed games like Uncharted 1/2 or Assassin's Creed, yet I don't exactly care for the story. Characters, maybe, but videogames have always had likable characters.
If anything, I think the quality of JRPG's has simply gone down. By focusing on stuff that doesn't matter so much (like cutscenes, gameplay gimmicks), and neglecting the basics, the games have become less accessible, and for most people, less fun.
Take Dragon Quest, for example - the formula is the same, hell, the series has hardly changed at all, yet it still sells extremely well. This is because its quality hasn't diminished. The same can probably be said for Pokemon (though I don't play it). Note that these games still play like the old ones - the same old turn-based combat that you refer to as bad gameplay.
The ones trying to be fancy, like FFXIII, are seeing decline for obvious reasons (not that I dislike it, but it plays nothing like the rest of the series, and alienates too many fans).
Hrm... I guess my overall point is, people don't buy games for the reasons you think they do. Story isn't as important as you might think, and the old JRPG's (FF, or Chrono Trigger), did not have bad gameplay.