Although it is a major factor, all of that can't be attributed to innovation, or even the "fun factor". There are other aspects such as intended audience, reputation as a gaming company, and notably, pricing of the units. So far, Nintendo has excelled in much of that. The 3DS will test Nintendo's idea to create a "high-end" handheld as a challenge to the PSP/NGP.
You do realize VGChartz doesn't use very accurate data right? For example, you can read on Wikipedia that "Sales figures on VGChartz are based on estimates extrapolated from small retail samples"
Here are the real sales data:
Here.
I did some cross checking, and it looks like most sites I visited differ on the sales data of the PSP. o.O The above source put the PSP at 66 million, while another had it at 61 million.
x_X
It's my job to help the next generation, and set a good example for them. And for that I'll gladly lay down my life.