Let's look to Japan for a few hard numbers to back up my speculation. Japan is a gold mine for salesage, being at the forefront of the console gaming industry and yet geographically smaller than California, making sales accounting quick and accurate. Numbers are according to VGcharts (love it or hate it) and corroborated by MC. So far D/P has sold a bit over 5mil, and soon it will surpass the sales of Ruby/Sapphire (5,357k), which went on to ship ~15mil worldwide. In comparison of consoles (DS vs GBA), the DS has already surpassed the GBA in sales within Japan (15,855,958 vs 15,326,384)*. So there you have it.
5
*These numbers fron NeoGaf