Ummm....where the hell has everyone been? They announced the end of the Grand Prix around 2 YEARS ago. The only reason any Grand Prix' were made in '08 was for fleet sales, thus the lack of a GTP this year.
The G6 is the Grand Am replacement, thus why the Grand Am disappeared around the same time the G6 popped up. G6 = 6th gen Grand Am. G8 = 8th gen Grand Prix.
As to why they changed the names, as much as it angers hardcore Pontiac enthusiasts, it DOES make sense from a business perspective. The general mass public perception of the Grand Am, Grand Prix, Sunfire, etc. is that they're piles of sh*t. Everything breaks on them, and they aren't meant to last. So rather than trying to convince people that these are GOOD cars now, they just scraped the nameplates altogether, and tried to start from scratch. I don't like it, but I can understand why they did it. Name recognition in this instance is a BAD thing, as most people that recognize these names want to stay AWAY from them, not coming running back to them.
As to the Firebird/Trans Am coming back, I don't see it happening. Remember, Pontiac is very close to being axed altogether, so I doubt they're planning on bringing back another gas guzzling V8 muscle car under that division during an era that has very little demand for one. It probably wouldn't go over too well with the whole bailout situation, either. If anything, the G8 coupe would make more sense (again, based off the Holden coupe), because at least that's a 2-door version of a preexisting car.