Interesting.I think DD sales for MH4 on 3DS were somewher near 250K last September.
MHP3 was a peak for many reasons, I can't see that happening again (as for some DS software peak)
Considering how great the buzz for 4G has been, one would have to assume that 5 (in whatever form it takes) will be hugely anticipated. Still, those MHP3 simply appear to be insurmountable.