I don't think it'd be too hard to make the flip-to-silence feature reliable on the Nokia. It already has a sensor to turn off the screen when you put it up to your face (or if you cover the screen with something).
So if you use that in combination with the accelerometer, then you should know when the phone has been flipped on its face.
Although, to be honest, it's not too hard to silence my Samsung Focus either. Just press down on the volume control.