But just because a game IS more accessible doesn't mean it can't still be difficult. My brother beat Mass Effect 1 at age 10 on easy but I couldn't beat it on the hardest setting after over 15 years of gaming. Not saying that ME1 is necessarily 'hardcore', but it does fit your pretty loose definition BUT still is appealing to and completable by a 'casual' gamer.
Besides, the more people play games and grow to like them because they're accessible, then there will be more fans of the medium. This could mean all those 'casuals' become 'hardcores', or that the industry becomes big enough to support niche genres, or that they then go discover classics like Castlevania or Baldur's Gate and decide they want mechanical challenges offered by 'hardcore' games too.
Also, there's a lot of indie developers catering to the 'hardcore' market, just recently I played Zombie Shooter 2, an isometric RPG-shooter that thoroughly whooped my arse on level 2 of Easy Mode. And I Wanna Be The Guy is...well, it's I Wanna Be The Guy.
Consider what Jim Sterling said too, that just because a game doesn't offer traditional difficulty challenges hardcore gamers may crave doesn't mean their isn't challenge there. Like trying to solve every puzzle in a Professor Layton game with no hints, trying a Solo Character Run in a JRPG, trying to get every collectible in a LEGO game, trying to do a No Damage Run on Kingdom Hearts. It's all there, perfectly feasible in the game mechanics.
http://tvtropes.org/pmwiki/pmwiki.php/Main/ChallengeGamer
As for more conventional challenges, what about superbosses in RPGs? Expert or equivalent difficulty modes? Trying to get Silent Assassin ranking in a Hitman game? Completing all those increasingly difficult side missions in games like GTA and its ambulance minigames?
To address the point of 'noob tactics' for a moment, developers are including characters and weapons that are easy for beginners, but deliberately balancing them so that once you get a firm grasp of the mechanics, you'll find it's actually inefficient for high level play and discard it.
http://tvtropes.org/pmwiki/pmwiki.php/Main/SkillGateCharacters
Also, no 'hardcore' titles? Off the top of my head I'd classify these fairly recent games as mechanically hardcore, and I'm not even a person with an interest in hardcore gaming:
Zombie Shooter 2 (and presumably everything else in the franchise)
Fallout: New Vegas' Hardcore Mode
Hard Reset
High level play on any beat 'em up e.g. Marvel vs Capcom 3
Dark Souls
Any halfway decent RTS/Turn Based Strategy/RPG e.g. Starcraft 2, Empire Total War, Civilizaton V
High level play on any decent multiplayer FPS e.g. Team Fortress 2
Bastion with the optional Shrine challenges
OK, so it's hardly a detailed list. But you may also have noticed I specified that many of these were only 'hardcore' as a deliberate choice to flick a difficulty switch or join a non-newbie server. That's the thing, FarmVille or Wii Sports Resort aren't the threat. They're being made for completely different people. It's the complacent studios and publishers playing everything safe and by the numbers. They're the ones making bland, cookie cutter games.
TL;DR 'Hardcore' gaming is far from dead, in fact between being able to buy/emulate classic games and actively seeking out challenge in newer ones, this is probably the best era of gaming for hardcores. Just because a game isn't made exclusively for your subset doesn't mean your needs aren't being served.