Fifa are saying that it can't be replayed because the referee made a mistake on a question of fact. If he'd applied the laws wrongly then it could possibly be replayed, but as he made a factual error then it stands.
Having said that, I actually have a feeling something will be done about this. I know FIFA are saying no, but I just get the impression this won't just go away. The play offs were rigged with the late decision to seed (although sure, even if there had been no seeding Ireland may have been drawn against France or Portugal, or even lost against Bosnia), and now this gets the French through, when it's blatantly obvious FIFA wanted them there. The Irish are generally well liked throughout Europe, and I think there's a LOT of sympathy for them. I wouldn't be surprised if FIFA announce that the French have agreed as a gesture of goodwill and in the name of sportsmanship to replay the match again. Would be awesome if they'd give Ireland a wildcard to the finals (thus ruling out any chance of France going out in a replay), but that would mess up one group in the finals so it's very unlikely.
We'll see.
Oh, and it's about time we had a single Irish team for the whole island, like they do in rugby. but that's a whole other story;)