Nintendo, Microsoft and since this new fiscal year, Sony, all release the numbers of consoles they have sold to retailers and they are released every quarter. When they release their financial statements for the second fiscal quarter (July through September) the life-to-date retail sales figures should be a decent number ahead of what ioi has for the end of september.
with Wii i would expect maybe 400-500k above due to them selling so quickly.
with 360 i am not sure, MS might have shipped a lot of extra consoles to retailers for Halo, thus meaning maybe 1 million plus over what ioi has....but if they didn't ship any extra than normal (ignoring haloSKU) then i would think due to the extra hardware sold through September there might only be a 600k-800k gap
PS3 might be anywhere from 500k to 1M over.....i expect they probably sold (retail) about 1-1.5 million more than last quarter...which was only 0.71M
and yes they are estimates, but they are not pulled out of no where, they are calculated in the same way that NPD/Media Create/GfK/Chart Track etc are, with the exception that those companies have more sources for referance (NPD has over 60% of American retail tracked, and extrapolates to make estimates for the rest.....not sure about iois percentage, but i think it's probably only 10-20%)
