Shin Muramasa
Metallic Stranger
I think it's because it was such a different game than what people were used to here in the West. It was a hack 'n' slash, but it was exceedingly methodical and not quite as fast paced as Capcom's other action series (DMC ), so I think a lot of people couldn't get past the idea of mashing buttons and actually taking their time against the monsters >_<
Monster Hunter is a hack n' slash, though not well-known until recently, but with a methodical combat system that usually requires planning and preparation with each hunt - makes sense, you're not going to go hunting with a bow and arrow against an elephant or use a shotgun on a poor, little wabbit. Cancels which are well-known in Capcom games are part of Monster Hunter. Soul Sacrifice is similar to Monster Hunter, though a little faster I think. Dragon's Dogma is much faster than Monster Hunter, but you still can't just mash buttons and hope to win since some monsters, especially the Ur-Dragon will pound your face into the ground if you screw around.
That said, in Devil May Cry games, you can get away with button-mashing until you reach higher difficulties. Same thing with Metal Gear Rising: Revengeance and I think Bayonetta. Hell, some of those games have "button-mashing" modes, the automatic easy mode.
I think the problem comes from the God of War games. I'm not saying they're a bad series; they're enjoyable. The combat does allow you to get away with button-mashing much more than other games. Then again, Kratos tends to fight crowds of enemies while Dante, Raiden, and Bayonetta tend to deal with multiple but not crowds of enemies. Also, first-world societies, tend to be fast and instant-gratification dependent. Not a lot of people are used to or want to deal with spending time on things. Why read a book when you can watch a movie? Why cook and spend quality time when you can go to a (fast-food) restaurant?
And this is why I think Dark Souls and Demon's Souls being considered difficult games isn't really true. I think it's that players have a tendency to just rush in and be able to take down anything that seems animate. Playing cautiously, which is what the games want you to do, makes the game challenging but not frustratingly hard, however, cheap things like the existence of Flamelurker still makes the games annoying. Freaking demon who's high on sugar.