That was before the DS suceeded in catering the casual audience. The PSP sold rather good, but more or less only to the "core audience". For people who don't usually pay attention to games it was way too expensive.
Which is exactly why it would be a stupid move from Nintendo to sell the 3DS for more than 200$. Something more expensive would be too expensive to reach the mass market, it'd probably be a successful core-device, but they would miss the casual audience; that audience which made the DS to the most sucessfull gaming device ever.
Nintendo can try to sell it for 250$, but thinking it well sell as good as the original DS line did just because the brand is strong, would be similar to Sony selling the PS3 for 600$ (a somewhat over-exaggerated comparison, but still similar)