PSP vs DS

There’s an interesting set of statistics on GameDaily today regarding the performance of DS and PSP in Japan and US.
I charted this data up in Excel to see what conclusions could be drawn. Here’s a comparison of top ten Japanese PSP and DS titles:
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And a comparison of top ten US PSP and DS titles:
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The first thing you notice is that the DS is trompling the PSP in Japan, at least in terms of software sales for the top ten titles.
However, in the US, the PSP and DS software sales are virtually neck and neck aside from the outstanding performance of Super Mario 64 DS – a killer app if ever there was one! (It should be noted that DS had a five month lead on PSP in the US.)
Two questions:
1. Why is the DS doing so much better than the PSP in Japan?
2. What will be the killer app for PSP in the US?
Innnteresting.