Because game reviews try as much to quantify the amount of enjoyment a game can have by just sticking to a small set of rules (The ever unchanging Graphics, storyline, gameplay criteria) which is basically a flawed system. It may work for traditional games, but are not suited at all for Wii games.

Well to put it bluntly, I stopped giving a fuck about scores given and now solely focus on what they write instead after seeing one site's (I can't remember which one sorry, was one of the major ones though) review of Tiger Woods 07. Comparing the 360 and Wii major points looked something like this (Scores aren't exact, but in the same ballpark):

360: Great graphics, half the content of the ps2/wii versions, basically a rehash of '06. Score - 8.5

Wii: Graphics don't compete with the 360/PS3 version, full content + extra mode for Wii, new controls are exciting with the fallback option to classic controls. Score - 7.5

So a game with half the content, nothing new but has better graphics is apparently the better deal. This isn't the only time I've seen reviews of this type, but this one has stuck with me as it was one of the worst.

I think the comment "Maybe Wii games have lower review scores because we, as an industry, still don't know what makes a good Wii game." sums up game reviewers entirely. They are too set in their old ways and aren't adapting fast enough to a fairly rapidly changing market.

Then again is the emerging market going to be reading these reviews anyway and are the only people who care about the scores one's who don't care for titles targeted at that market?

 I don't know. The writer states "If we attempt to level the playing field and only look at the top 10% of all games on each system, the picture evens out a bit for the PlayStation 3 and Xbox 360, but the Wii is still significantly behind:" yet the Wii is only 3 or 4% behind the others. I wouldn't say it's significantly behind.

It's the amount of shovelware, all there is to it, reviewers aren't as forgiving today as they were back in the beginning of the PS2 era either, people have learned to expect certain things from games now, and shovelware doesn't do it so it gets lower scores then old PS2 shovelware did.

@HappySqurriel

That's accurate as well but look, the PS3/360 are significantly stronger than the Wii. No argument there. So the games there are going to require much more than the average game for the Wii. That's why development costs for the PS3/360 have skyrocketed from the last generation. If you're putting a rumored $70,000,000 into a certain game, you'll want to put the best devs on the job to make sure the money is not wasted (although some of it probably will). The leaves what for the Wii? But yes, publishers put so much money into the 360/PS3 because they initially thought that's where the money is at. Since then, I think they have learn their lesson and is quietly allocating resources to the Wii. I could be wrong.

On top of this, the top 10% of Wii games represents 20 games while the top 10% of PS3 games represents 11 games, even if the Wii had identical scores (when you removed shovelware) this calculation should work out in the PS3's favour.

i think aot of reviewers are just being lazy about it--they pop it in look at it compared to halo3 or resistance then decide based on that insted of the game itself

 this and the fact that Wii caught third parties with their pants down

The fact that all those charts are done in an incorrect manner means I simply skipped over the entire article. Im not going to read something when the person makes misleading graphs on purpose. Of course average review score difference looks like a massive difference when you put it on a graph with a scale of 16 that should actually be 100.

64,70,73 out of 100 isn't a big difference. Especially when the systems don't have the same number of games.

Maybe they should have seen how many 90+, 80+, etc games each console has? Though either way I think it would favor the 360 (it's been out longer) and the PS3 (to an extent), simply because 3rd parties thought they would be the winning consoles, and released more and better games for them. I'll wait until the end of the year before saying that the Wii's "situation" won't get better.