This is a pretty much constant theme in Nintendo Discussion but I haven't seen a breakdown of actual sales anywhere in said threads.

These are the million selling Wii games according to VG Chartz (some data is missing but it's the best we've got to go on). I've designated them hardcore or casual. Feel free to disagree as it's a crappy and arbitrary distinction anyway but one the industry is obsessed by and probably will be for a while yet. If I can imagine my parents or a non-gaming friend wanting to play it I've labelled it casual. So basically casual here means accessible. Core gamers may also like it. IMO MK, Sonic, Lego Star Wars and GH3 don't fit into either because they have very easy and very core aspects so I've labelled them "both".

Pos	Game	Console	Publisher	Hits	Score	Sales
1		Wii Sports		Nintendo	48,616	7.86	23.66m
2		Wii Play		Nintendo	26,312	6.83	12.49m
3		Super Mario Galaxy		Nintendo	135,232	8.12	6.56m
4		Super Smash Bros Brawl		Nintendo	89,930	8.03	5.38m
5		Mario Party 8		Nintendo	24,502	7.46	5.20m
6		Mario Kart Wii		Nintendo	44,141	7.78	5.12m
7		The Legend of Zelda: Twilight Princess		Nintendo	36,734	8.26	4.81m
8		Mario & Sonic at the Olympic Games		Sega	8,173	7.76	4.44m
9		Wii Fit		Nintendo	46,132	7.86	4.37m
10		Guitar Hero III: Legends of Rock		RedOctane	18,992	7.69	2.70m
11		Big Brain Academy: Wii Degree		Nintendo	8,926	7.41	2.37m
12		Wario Ware: Smooth Moves		Nintendo	6,596	7.38	2.34m
13		Super Paper Mario		Nintendo	14,731	7.79	2.34m
14		Link's Crossbow Training		Nintendo	14,698	7.34	1.98m
15		Carnival Games		Global Star	10,512	7.24	1.86m
16		Mario Strikers Charged		Nintendo	15,772	7.80	1.65m
17		Resident Evil 4: Wii Edition		Capcom	47,933	8.13	1.60m
18		Metroid Prime 3: Corruption		Nintendo	52,214	8.09	1.37m
19		Sonic and the Secret Rings		Sega	11,720	7.75	1.37m
20		Rayman Raving Rabbids		Ubisoft	6,874	7.66	1.34m
21		Lego Star Wars: The Complete Saga		LucasArts	10,411	7.75	1.24m
22		Resident Evil: Umbrella Chronicles		Capcom	33,040	7.77	1.22m
23		Rayman Raving Rabbids 2		Ubisoft	11,983	7.75	1.20m
24		MySims		Electronic Arts	6,918	7.25	1.07m
25		Red Steel		Ubisoft	5,658	7.04	1.05m

Wii Sports - casual

Wii Play - casual

Super Mario Galaxy - hardcore

Super Smash Bros Brawl - hardcore

Mario Party 8 - casual

Mario Kart Wii - both

The Legend of Zelda: Twilight Princess - hardcore

Mario & Sonic at the Olympic Games - casual

Wii Fit - casual

Guitar Hero 3 - both

Big Brain Academy - casual

WarioWare - casual

Super Paper Mario - hardcore

Link's Crossbow Training - casual

Carnival Games - casual

Mario Strikers Charged - casual

Resident Evil 4 - hardcore

Metroid Prime 3 - hardcore

Sonic and the Secret Rings - both

Rayman Raving Rabbids - casual

Lego Star Wars - both

Resident Evil UC - hardcore

Rayman Raving Rabbids 2 - casual

My Sims - casual

Red Steel - hardcore

I'm sure people will disagree with some but if we go with those that gives us 13/25 casual, 4/25 both and 8/25 hardcore.

Total sales:

Casual - 63.97m - average of 4.92m per game. If we exclude Wii Sports (but remember it's what persuaded to vast majority of casuals to get a Wii in the first place) then we get 40.31m - average of 3.36m per game.

Both - 10.43m - average of 2.61m per game.

Hardcore - 24.33m - average of 3.04m per game.

I'm not pretending this is scientific or fully representative. There are lots of casual games languishing at the bottom with very poor sales and everyone is going to disagree with at least one of the categorisations I've made. Casual games are also likely to make a profit off lower sales than a hardcore game could. But it does show where this "the Wii only sells to casuals" comes from. Even though the average sales per game is roughly the same for hardcore or casual there are more casual games shifting big units, leading to much larger total sales of casual games. If you're a publisher like Ubisoft wanting to make fast money it's easy to see why you'd get the idea that casual is the way to go. Casual doesn't have to mean bad though. There are several games I've labelled casual that I'd be happy to play and I'm sure most people on this board would too.

Nice analysis. Furthermore, if we remove Wii Play too (it's unclear how many people would buy it were it not for the remote), the average goes down to 2.53m sold units per casual title.

Defining a game (or a gamer) as "Hard-Core" or "Casual" is meaningless because it trivializes both the game and those who choose to play it ... The vast majority of Million selling Wii titles are conventional games which would not seem dramatically out of place had they been produced for the Gamecube or PS2.

How many people complained that the PS2 dance mat games were 'too casual' and that they were 'destroying the market' like Wii games are? None.

It all depends on how heavily the game is marketed or if its an established franchise. If it isn't either, the game must be really good and sell through word of mouth.

Oh Jesus........
There are bloody & non-bloody,
There are traditional & non-traditional(Wii Fit)
There are kiddie(ok,ok.. kids friendy), non-kiddie(mature) & granny(suitable for elder)

There are Nintendo & non-Nintendo, & the answer will always be Nintendo

 dance mat = Guitar hero.

how many people here claiming GH3 is "destroying the market"??? none

How many people here claiming that Carnvial the game is doing the same? Well, can't speak for others, but I have.

Sadly most 3rd parties have the same understanding as the OP and thus continue to fail.