There certainly is a posibility that the 3DS launches at $250, no doubt about it, but it's also the same posibility that it'll be $200
Iwata has stated it'll be higher the DSi, that could mean higher than now, or after a price drop we don't know. I'm personally leaning towards $200, but $250 although pushing it, wouldn't surprise me.
It's different with the Wii, since people see more value in home consoles, because you only need one for multiplayer and parties. Since handhelds are more personal devices, charging that much money would be a mistake.