Slipping release dates for games (all of them)

I got yet another email from Amazon today saying that one of preordered games was now going to be later than the original date.
Preordering is great, but it does mean you notice more when an item slips, namely because Amazon are great and tell you :-)
Grand theft auto iv slipped to next year, Assassins Creed by a few months, Spore into 2008 the only one left on the list is the mighty Halo 3. It may be that bungie and the launch parties that scoble was bloggin about, may actually hit this date (though of course it was supposed be a long while ago as I remember).
Some of this may be to whip up demand amongst us gamers that like the new and the shiny, or to maximize those christmas profits, or post christmas blues when people buy games.
Either way its a pain, but not as big a pain as wandering into a shop like Game, seeing the box on the shelf, walking over to pick it up and then noticing the damn sticker saying "coming soon - preorder now". If I wanted to preorder I do it on the web!
I am a techie, and I know deadlines slip, development is an art form and fills the time available. However, why not just have a realistic date, I end up "seasonally adjusting" every date I see, but that should not be my job :-)