Dude all that proves is that review scores mean shit all.
Enjoy the game. You don't need other people to tell you that they reckon Reach is a 9.3 game.
For me Transformers War for Cybertron was an absolute blast to play and look at where that's sitting on Meta. 76.
Just one thing though from your post, Halo 3 has like 90 reviews on Meta while Reach only has 30 right now. By the time Reach reaches 90 reviews on Meta, it'll either be on 94, 93 or 92.
94 if more reviewers give more 10/10. 93 if review scores range more 9-9.5 and 92 if more reviews give 8/10.
And since you brought up the topic, it continues to bug me how on earth no game is able to top GTA IV on Metacritic of 98. Is GTA IV really that God like that it's on a 98 on both consoles?