I never understood this arguement. So Nintendo do not pick the most powerful CPU/GPU available. Why does that really matter? It is a lot more powerful than the device before it and it has amazing games on it still.
With a handheld the most important number, to me, is battery life. I still feel that Nintendo (and Sony) could do more by using a more efficient or lower power chip and get a couple more hours out of the device.
Then again I do not care that much for graphics so perhaps my opinion is in the minority. There are several things I would change about the 3DS if I could but upping the processing power is not one of them.
Less power means longer battery life, and it doesn't matter as long as the games are fun. The game being fun is much more important than how new the processor is.
It's been like that for a long time. I'd argue that for mobile devices, you don't really need that much power anyway to make something fun and adapted to the format. The PSP is still selling well in Japan and developers are still making game for it to this day.
In the end, it's the experience of the games you care about that matters.
I bought my 3DS for basically 3 games, and while the graphics don't compare to my phone or tablet, the fact that I can even have them in a portable form factor prevents me from caring that it's underpowered.
It is like the Mac/PC or Android/iPhone hardware question. If someone cares how many cores their computer has then they will probably shop for an Android phone with a fancy processor. Most Mac buyers pick "the cheap one", "the middle one", or "the fast one" and couldn't tell you how much ram, or which processor is inside their laptop.