One reviewer might only rate highly hyped games which he expects to be good (nearly all fall to 60-100 range) and other reviewer tries out pretty much everything he encounters to find out those lone gems among less well-known indie games, etc. (let's say ranging from 20 to 95). We can't just take a bell curve of each and say "Game A is slightly above average on first reviewer's scale and Game B is slightly above average on the second reviewer's scale... so they're probably about equally good!". Sure, with large number of reviewers, you can still see which games do well and which won't but you have lost at least as much precision as you would have if you hadn't taken the bell curve in the first place.
That said, I don't know if reviews are that relevant anymore. I am active gamer but don't remember when was the last time I read a full review... There have been two times recently when I bought newer games from series I had played years ago (Cossacks and Anno 1602). I just wanted to take a quick peek on whether the games were considered about equally good, better or worse than the ones I had liked and whether they were very similar with just better graphics etc. or if some major concept had changed. That consisted mostly of looking the games up on Wikipedia and quickly glancing the first reviews I found using Google. I think I also checked the metascore, but it was more among the lines of "I'll buy it unless it turns out to have metascore under 60 or something". I didn't use that as exact metric.
Most games I buy are ones recommended to me by my friends, those recommended by blogs I follow (e.g., the Penny Arcade guys' news feed... you could consider those reviews, but they don't mention the games they hated, don't give scores, etc., just mention "Hey, that was pretty good. Try it out.") or those that just seem fun and don't cost much (When I noticed Orcs Must Die on Steam for under 5 euros, I didn't start doing extensive research on the critical acclaim of the game.)