You forgot to mention that the DS sold 1.6 million and the PS2 1.4 million in December in the US as well, according to the NDP.
The DS too, with its pointless second screen and hilarious touchscreen controls (using a stylus to draw stuff on the screen, for games? ROFLTUNASANDWICH), is also a gimmick, only made for non-gamers.
The DS is also the fastest-selling console worldwide ever. Even the mighty PS2 didn't grow this fast at the same point in its life.
If you look at the top 30 games sold this week in Japan, 26 of them are on Nintendo systems. If you look at the top 15, they're all Nintendo.
However, as Volo says, catering to a new market while still providing 'hardcore' games, at the cost of having weaker specs, does not print money. Even if you're selling really well in all regions.
Not to mention that among the top selling DS games are completely traditional games like New Super Mario Brothers and Pokemon. Just because a system allows for new control schemes doesn't mean you can't make traditional games.