Alot of so called hard core games ie FPS, RPG's and Strategy Games all clear have very high production cost. however I think most are using the same engines now whhich will keep the production cost down, its mainly the art design that costs.

How ever I think the sales will go down because people will get bored witgh hard core games, as they are becoming all the same, there is a lack of imagination.

I agree with everything the thread maker said, but I'd like to extend the problem to gameplay content.

One of the other critical differences between hardcore gamers and casuals is their competence with specific genres.  Let's say there are two differences in between hardcore gamers and casuals:

(1) hardcore players proceed through "easy" segments of the game faster
(2) hardcore players want more challenging semgents.

Like graphics, if you want to appeal to the hardcore audience in addition to casual audience you have to spend more money to satisfy the hardcore.

Consider Super Mario Galaxy, a game designed to appeal to both audiences. 

In order to satisfy the hardcore gamers, this essentially means Nintendo must program more content in order to deal with (1); if SMG had ended at 60 stars after only 7 hours (for them) of gameplay many hardcore fans would refuse to purchase the game and consider it a rental instead as many people say should be done with Heavenly Sword.  But in order to satisfy (2) Nintendo must also program more difficult segments.  Now in order to limit the frustration to the casual audience and since everyone wants to play the finale, Nintendo must make these more difficult segments optional (E.g. you only need 60 stars to complete the game). 

Essentially, in order to appeal to the hardcore audience in addition to the casual market you need more content for (1) and some of that additional content needs to be optional for (2).  Since you have to pay someone for all that additional content, it raises the cost of your game.

One crucial difference between gameplay and graphics though is that you don't need any gameplay oriented towards less hardcore players if you're willing to sacrifice that large portion of the market.  You can go with all hardcore content.  Some companies make this sacrifice, programming only content geared towards hardcore players or loyal followers of a particular series or genre.  I'm sure everyone has their own examples, but for me, I'd say the Tales series from Namco, the fighting game Guilty Gear, and many other "cult" classics take this approach.  But that's also part of the reason they're cult classics and not universally aclaimed classics : (.

Hopefully, games like Super Mario Galaxy though will show that having content aimed at all audiences satisfied can pay off.  (Crosses fingers for better NA and other sales than Japan.)