They are not moving away from the casual market. Have you even seen the WiiU adds lately? Those are aimed at the casual market.
No casuals buy a brand new system at 350$ at launch. Nintendo knows this. Casual doesnt even know what the WiiU is. Nintendo can't possible hop to get the casuals w/o getting some market penetration first. When more ppl buys the system (mainly cores) the casuals will know what the system is and thx to word to mouth they will start buying it.
The Wii U commercial they are broadcasting here is beyond ridiculous. The voice sounds exactly like a parent talking to a ~4 year old kid, even when showing ZombieU... Seriously, it's so bad and inappropriate that I find it awkward to watch everytime it shows up on TV. At least their old SNES/N64 commercials were fun to watch, and made fun of the kiddyness. What we have here is basically a parent telling his/her 16 year old offspring to play with the nerd kid that just moved in next door (the Wii U), instead of going to his old "cool" friends (Xbox 360/PS3). Needless to say, I'd be surprised if one single person who consider himself a hardcore gamer would be convinced to buy the system after watching that commercial.
Also on topic: I really don't see how Nintendo has left or "moved away" from the casual market. They will still have Wii Fit, Nintendo Land, Mario Party, games like Wii Play, etc. for the Wii U. Broadening their target audience is only a good thing, if executed appropriately. Xbox 360 made a great attempt with the Kinect, for instance. Nintendo should be able to do something similar, though it should take several generations in their case to convince people that they are a "hardcore" platform to be reckoned with. Mario is the symbol of casualism, after all.