Ugh, the "handhelds aren't consoles" is such a bad excuse, I don't see the logic behind it at all...
There's a difference between stationary/home consoles and handheld/portable consoles, but both are consoles. I would even go as far as to say it's perfectly fine to compare handheld and home console markets, I mean, just take a look at Japan and you see what I mean.
Anyway, I guess the thread is about Wii vs PS2 and which of them will be the best selling home console. I bet it depends on Nintendo and how they will support the Wii over the next few years. If Nintendo continues to release system sellers, doesn't get overrun in the upcoming motion war and doesn't release a new home console within the next few years then I can see the Wii becoming the best selling home console. It will be close though.