Take Japan out of the equation, and then look at the numbers; esp wrt to software sales and yes, an argument can be made that the 3ds is underperforming.
So talking about handhelds by removing one of the largest markets dedicated to handhelds makes sense how? that is like saying the 360 isn't selling well if you ignore America's sales.
Why are you comparing consoles and handhelds? The markets have been proven to be nothing alike.
Same is applicable to the PSP (76million units since 2004)... I would still argue that console market and handheld market are not entirely different, which is why Vita's owners in general own PS3s as well.