I expect that under more normal economic climates they probably would have phrased their predictions as:
Wii: 20 Million +/- 4 Million
PS3: 10 Million +/- 2 Million
XBox 360: 10 Million +/- 2 Million
If they had done this no one would have cared because they would (essentially) be saying that they expected sales to (basically) continue as they have been ...
In the current economic climate they will base all of their sales off of the bottom of their prediction scale and (throughout the year) as sales out-perform their expectations they can always make an correction to their financials.







