This question is at most 4 months too late, at least 6 months too late.
July 2007 answered this question and September 2007 echoed it like that Ricola commercial (international visitors see reference here: http://www.youtube.com/watch?v=PFaO0ALa0Hc ).
When Wii got evens stevens with the 360 in July on their way to passing them for the rest of the summer, it was already a sign that they were unstoppable. They caught a system which was the only 7th gen console representative for a year. Caught a system which had been out for a year & 8 months (20 months) IN 8 months...FLAT. Caught 'em in less than half the time (about 2/5 the time to get it more exact).
That was doom right there. MS price dropped the 360 around that time to try to offset both Nintendo and Sony. It worked against Sony. It didn't work against Nintendo. And while 360 began to pick up brisker sales than in the 1st half of the year, Nintendo under supply strain was still making monkey uncles out of MS on the charts hardware-wise.
September 2007 was the final test. This was Halo 3. The biggest game in XBox history. They even made a new flavor of Mountain Dew for these guys and there had never BEEN such hype for a game. It came out & set records selling over 3 million worldwide almost 4 million in the first week ALONE. It predictably boosted XBox 360 sales, doubled 'em in USA, and showed the power of MS having this year-long headstart on the competition. Along with the supporting cast of Bioshock & friends XBox 360 looked to be champ.
Nintendo's Reggie Fils-Aime Regginatored the sentiment that they weren't at all worried about MS's surge. That MS had already fired their bullet and Nintendo was prepared to fire its bullet all throughout the holidays. Said it calmly too while he polished his gun.
By VGChartz estimates, by NPD's estimates Microsoft's Hail Mary DID push them above Nintendo for the first time in forever...but by how much?
A measly 20,000 or so.
MS's day in the sun only pushed them about 20,000 over Wii in a month where Wii did nothing at all spectacular. Metroid Prime 3 launched in late August and sold steadily. It could not factor too much into Wii's hardware push selling more to those who already owned the system. Not only did Wii do nothing at all special but Wii's numbers actually ROSE to their highest monthly point SO FAR at that time. Microsoft with their biggest push ever beat a quiet Nintendo who actually rose in this lull by just 20,000. On its best day Microsoft barely beat Nintendo on its worst day event wise. Not factoring in the supply problems that Nintendo faced which if controlled may have ruined MS's best day.
After Microsoft went back to normal the next month & Nintendo got even stronger it was apparent that MS could no longer stop The N only being able to hold on as best they can in this Nintendornado.
The only card left to play is that MS at least in USA has stronger software sales than Wii at the present moment. And that card will be trumped in 2008 as Wii enters its full 2nd year. By Holidays 2008 all these arguments about challenges to the Wii will be muted as it all becomes apparent that Nintendo's real name is Cain Marko (get out your wikipedia, children).
The point of no return has long been passed. No one can stop Nintendo in 7th gen. Fight for the runners-up position 'cause the contest is officially over.
If you still don't believe come see me in July after Wii Fit has made its debut & Nintendo's supply problems have gained inroads. I guarantee you it'll be clear then.
John Lucas