Actually, now I'm wondering, what does the nunchuck do about it? Since people plug them right in, don' they?
Now that's an excellent question. My guess would be that the ASIC in the nunchuck does some level conversion.
The nunchuk doesnt have a LIS302DL. I think it is a LIS3something and it is probably 5V. The LIS302DL has on chip i2c.