Okami wasn't severly undertracked. Based on Capcom (Sev's) statements VGChartz is even high on Wii version sales. To top it off, it just flat out wasn't tracked, as VGC doesn't have NA/EMEAA sales for the PS2 version and doesn't have EMEAA sales for the Wii version.
anyways, to address your points
1) PS2 had over 110m units sold when it was released. I wouldn't count the DS with 135m sold as a much larger potential customer base. While PS2's were bought to replace older broken models, DS's are bought for multiple people in the same household.
2) nintendogs has nothing to do with Okami
3) I sorta doubt it. Capcom doesn't seem to care to much about Okami.
4) Lower price for games hasn't equated to higher sales. DS has 105 million sellers comapred to the Wii's 85. I'd say that is fairly close for the larger install base and extra years on the market. If you want direct comparisons look at a lot of the liscensed games which sell better on PS360 than any other system (like Spider-man 3 for example)
5) Pokemon Black/White just came out. I doubt many people will see Okamiden as the DS's last hurrah and Nintendo has their own games to advertise.
Anyways, I can see Okamiden getting 200k max in Japan, and 300k each in NA and PAL territories for 800k total. I'm not rulling out breaking 1m but it'll have performed extremely well.
