Back in 2007 E3 wasn't held till the second week of July, and Halo 3 was a major focus of that show. Microsoft positioned the title to move millions of consoles. They fully owned the game, and thus got all the profit. The playing field at the time was far slimmer across all platforms. Which allowed Halo 3 to basically go gang buster unopposed.
Now to this year E3 was basically held a month earlier. Meaning it couldn't readily tie in with the fall advertising. This year Microsoft feels that Kinect is what is going to move consoles, and it was the major focus of their E3 showing. They don't own Halo Reach outright, and thus they don't get all the profit. The playing field this time around is thick with high end titles, and Microsoft must provide advertising not only for multiple titles, but a new peripheral. Halo Reach will have to deal with stiffer competition.
Your basically comparing Apples to Oranges. Other then the Halo name the situations are hardly alike. That all said you can also say that Microsoft doesn't need to sell gamers on Halo anymore. The game is going to sell incredibly well without a massive advertising push. Halo Reach just isn't going to sell the 360 this year. Any true Halo fan bought the console years ago, but they do need to sell consumers on Kinect being something that they have to have.
