nexgenwars frequently has adverstisments on the top of the page for PSPs and other Sony products (as well as Xbox). I somehow doubt that a MS financed project is running ads for Sony. Just a hunch.
And, yes... ngw's figures for Wii and PS3 are as absolutely as every bit screwy as this site's Xbox 360's figures.
My biggest question about this site is that apparently the guy who runs it goes by the handle "Wii_gamer" and the Xbox 360 figures are horribly out of line with every other professional analyst. I can't help but wonder if the 360 is being lowballed here to make the Wii appear better.
I suspect that NGW is being run by somebody in love with the Xbox and vgcharts is being run by a Nintendo fanboy. In each case they don't screw with the numbers of their beloved console, but with the other consoles figures.
So, my personal opinion is if you want the absolute most accurate stats, go to NGW for your Xbox 360 stats and get your Wii stats from vgcharts.
I'm not sure where to go for your PS3 stats. I don't think anybody likes them. Perhaps I'll corner that market and start a site. I'll skew all the numbers anyway I want!
How does this look?
Xbox 360 - 7.5 million
Wii - 2 million
PS3 - 2.1 million