I don't believe there was any particular need for any of the leaders to be at the announcement. But then again, I suppose the Olympics would be a pretty big economic asset (poor Greece, that didn't exactly work out, did it?).
The visit would be, like a lot of thing the heads of state do, mainly ceremonial/respectful since the Olympics are supposed to be a symbol of global harmony/ coming together.
But, while Bush had no particular reason to be present, I don't think you're justified in using the G8 Summit as an excuse. After all, Blair is a lot more involved: he is HOSTING it!
As a non-Brit, I found Chirac's comment's hilarious
. I believe they went a lot further than just saying the British can't cook. I think he said that no one whose food was that bad should be trusted and that the only contribution Britain has made to European agriculture was Mad Cow disease