That's impressive, I didn't know they had sold so well.
What I meant by 'not mass market' was more the developers' reckoning of the game's appeal. In practice, a lot of people imported the game from Japan to play it in the US because they didn't even think it would get released here! Then, when it came out, IIRC sales dramatically outpaced the publisher's expectations and they had to rush to make and distribute more copies.
Given that Demon's Souls was conceived in Japan, I would describe it's mechanics as very fitting to the huge group of core-gamers there. The western success is surprising, I give you that, especially considering the rather meager marketing of the first.
http://www.vgchartz.com/yearly/2011/Global/
These games are surprisingly mass-market.