Xbox 360 sales are much higher than their normal rate. This is Microsoft's best time of year, and they're coming off the release of their once-in-a-generation Halo 3 release. And now Bungee went third party.
Nintendo sales are in a slump. It's reasonably safe to assume they *will* pick up for the holiday season, and Nintendo will be selling out everywhere again. It's also reasonably safe to assume that Super Mario Galaxy will hit and make a huge splash, and it will surprise a lot of people who aren't watching games closely. The game looks so amazing I can't help but wonder how the general public will be affected by it.
Nintendo's baseline sales in Japan are disconcerting, but we have to remember what Nintendo has done so far as well as what they haven't done: their biggest franchise release and a price drop. They've got Mario coming and they've got Smash coming. This will wake up a lot of Wii owners who have fallen asleep.
You're taking a snapshot from a point where Microsoft is abnormally strong and Nintendo's strength is in a slump and then you are wondering outloud if this will be the new way things go, or if this is part of a trend. Obviously, Microsoft is doing well due to its big release, but Nintendo's strength has yet to be truly tested. Give this battle a little time before you try to determine whether the war is changing fates.