The thing is these pre-retail polls really mean nothing in the long run. GameCube also fared favorably compared to the PS2 in similar polls.
Not to say the DS will perform as poorly as the GCN has in Japan, but just to point out that this really means nothing.
In the end, I think we're not going to have a clear picture of really whats happening until about next spring, because the initial DS and PSP shipments should sell out quickly just due to the launch period.
Once both companies settle down into the market, get adequete supply, and the second wave of more polished software titles start coming out, then I think we're going to see either the DS or the PSP start to pull ahead.