That's not exactly out of range of Vgchartz estimates.
For example using Vgchartz data and 5% uncertainty:
360 at 19.78 million with 5% uncertainty = 18.79 to 20.77
PS3 at 14.41 million with 5% uncertainty = 13.70 to 15.12
Now let's say you work for Sony and are optimistic about PS3 sales and pessimistic about 360 numbers:
18.79 - 15.12 = 3.67 million difference