Those charts are only of dedicated gaming systems. Its quite possible for handhelds to slide into obsolescence alongside consoles.It's happening in Japan? The general consensus seems to be that the country has gone handheld crazy over the past few years. The 3DS tops the sales charts every week almost without fail, and often by a massive distance. The Vita now seems to be taking 2nd place as well.
The 3DS isn't doing as well as the DS, the PSP is certainly no Vita. The portable market is significantly down generation over generation.