I guess DS will pass PS2 eventually - although I believe strictly speaking if you go by shipments and sales this site is apparently not tracking at the moment it hasn't yet so the news may be premature - but I just don't see it as anything amazing.
The DS is a handheld. A great one, I've bought two myself, but it's comparing a handheld to a home console. I just don't find a handheld managing to sell more than a home console particularly impressive - if anything I guess I'm surprised it doesn't happen all the time.
I may just not get the demographics of handhelds right - or perhaps their growth has been slowed by smart phones, etc. this gen vs the general rise in gaming industry, but so far as I can see in theory they should sell more than consoles easily, particularly due to families. I know friends who buy one console then four handhelds because they have four kids. Really handhelds should have a huge advantage in potential userbase as they tend to be one to one for owners whereas many consoles are one to many for users.
Maybe I'm missing something.
Try to be reasonable... its easier than you think...