Not sure how I feel about this.
On one hand they are spinning it as a way to add content right up to release. On the other, it's essentially a broken game on a disc that doesn't work unless you update it as soon as you put it in your console.
In reality, it won't affect many people unless their servers are broken on day one but I doubt that would be an issue. There probably won't be that many people with Forza 5 on launch day.
The real problem is that people are essentially buying a game that doesn't work. It's not new for people who buy PC games in a box that need to be patched to work but this isn't an online only game.