You guys are right but what it will show is how fast the PS3, and more so, the Wii will start catching up to XBOX 360 sales. It's displaying present market share and so it is accurate. Naturally the 360 will have a larger market share because it has been out longer but right now 360 sales will start to fall dramatically and PS3 and Wii sales will rise
dramatically thus leveling out the market shares.
This is also quoted from the site
Remember, these numbers are only estimates, but they are constantly monitored and updated to assure the closest estimates possible for the Xbox 360, Playstation 3, and Wii.
This clarifies the question as to how accurate the numbers are so no, the number will not immediately go up if you were to buy an XBOX 360 right now. Although seemingly pinpoint accurate, the numbers are still generalizations.