In my observations of console sales for the last say six years, there has always been 1 console that is far out in the lead and usually has the most momentum. Sales for the competing system/s catching up for the most part happens during the busy season. For example, during the month of May the week of the 11th, the PS2 had a hardware advantage over the xbox of 7,384,671 in the Americas, and sold 55,124 units, the xbox sold 26,015. The xbox would never gain enough momentum to ever catch the ps2 but did outsell the ps2 during 2 of the biggest weeks in Dec 2004, again to loose momentum at the end of January 2005. This spike in sales was in part due to the release of Halo2 witch killed Metal Gear in sales but wasn't enough to fight off the onslaught of games the PS2 had going for it.
In another example of hardware momentum, the xbox in Sept of 2004 had a hardware unit advantage over the gamecube of 1,183,096 in the America's. The week of the 25th the xbox sold 63,012 and the gamecube sold 27,506.
Looking at the Others market we can take an example of week 4, 4/30/2005 (A slow week). The xbox had a hardware lead over the gamecube of 2,526,847 units. That same week the xbox sold 17,145 units and the gamecube sold 8232, and last but not least the ps2 had an astronomical hardware lead (kinda like the wii is on its way to having), it sold over 100,00 that same week.
This generation the ps3 has an insermountable lead over the 360 in Japan, witch I feel is its only hope to ever catch up the 360's mammoth lead in the America's. The Holiday fueled momentum it has in Others is not enough for the ps3 to usurp the 6+ million lead the 360 has in America. Also take into account that Microsoft is not stupid, they know the momentum they have already made and have already publicly stated that Europe is key battleground. http://www.gamesindustry.biz/content_page.php?aid=31694.
Last but not least, price must be taken into account. If we are to compare this generation to the last, the wii is the ps2 of this generation the ps3 is the xbox and the 360 is somewhere in between. The wii is a hardware force and has momentum that may never slow down, and will be able to go toe to toe with any of the next gen hardware as far as price. The 360 in America is a Software force and ain't to shabby in Europe either with an almost comfortable lead over the ps3 in the meantime. Microsoft will milk the 360 at the price that its at now to continue profiting on software sales until the last minute, then BOOM price-cut, (and the next one might actually be a pretty significant price cut). Unless blueray and cell architecture get stupid cheap Sony won't be able to compete on the price side of things if 360 hardware is cut significantly. Time will tell, but at the momentum the ps3 has, as of now, it'll be a looong time before it catches the 360.
