Yeah and that was a computer generated teaser trailer, similar to the one we have for Halo 4.
But you can't really compare Halo 3's marketing campaign to Halo 4.
The digital world is extremely different now than it was in 2006.
Word of mouth is an extremely powerful method, especially with tools like twitter and facebook.
Information can pass to various different groups of people very cheaply and very fast... depending on how interesting that information is.
The more hyped the subject, the more interesting the news.
The longer they delay Halo 4 news, the greater the hype, the faster it will spread.
The game actually living up to the hype is another matter.
But they are obviously willing to risk that, so you know the game is gunna be good!
But of course all of that is just my assumption.
Who knows what they are planning.