I think there is something peculiar in the french culture that leads us to only play well in two precise situations:
1. if it leads us to be called heroes at the end of the game
2. if we have been super shitty the game before
It's an interesting theory (and you make quite a convincing case in its defense), but I think it leaves aside a crucial element that might make it irrelevant this weekend: it has never been tested in a RWC final. Point 1 would obviously have applied to the 1987 and 1999 finals, but definitely not point 2 (we played fantastic semis both those years).
From my point of view, leaving aside New Zealand's obvious superiority (so far...) in this tournament, there's a key factor that needs to be taken into account: France has never shown that it has what it takes (in terms of talent, guts, desire, etc.) to win a RWC. We have played three truly great games in RWC history (vs. Australia in 1987, vs. New Zealand in 1999 and 2007), but we've also had our share of sub-par performances, and most importantly we couldn't even make it competitive in the two finals we played: we were dominated and outclassed by both New Zealand in 1987 and Australia in 1999.
The counter argument is obvious: these are different times with different players and a different coach; and of course, following elgringo's logic, we should do a lot better this time around because there was no display of brilliance and panache in our semifinal this year (as opposed to 1987 and 1999).
Sure, why not? But I believe, perhaps a bit irrationally I'll be the first to admit, in the forces of history and tradition: we have a losing culture (yes, a bit harsh, but there's no other way to put it IMHO) in RWC that was started in 1987 and has continued throughout the years; and the circle of defeat will not be broken easily. Our soccer team did it in the 1998 WC, unexpectedly crushing favorites Brazil in the final, so maybe there's a parallel to be drawn here: could we possibly beat mighty New Zealand on Sunday? The pessimistic in me doesn't see a rugby equivalent of Jacquet and Zidane in our team this year; and worse, the fantastic "esprit de corps" we had from day one in the 1998 WC and that eventually lifted us to victory has been spotty at best (and I'm being charitable) in the 2011 RWC.
Let's face it, when it comes to RWC, we're a second-tier nation--arguably the best of all second-tier nations, but it's a giant step to rise to the level of the Australia / New Zealand / South Africa / England quartet; and a giant step, especially given what we have shown so far this time around, we are most likely not ready to take.