labingi

This is a very good question. I know nothing about Emma from comics canon, but since every mutant seems to have different powers, my guess is that Charles and Emma have telepathy that works differently.

I tend to see Charles as having a mind that is open to surface thoughts/feelings by default. To go with an image I used in fic, reading minds (superficially) is a bit like having his eyes open. Not reading minds is a bit like closing them: not hard to do but hard to sustain and basically unnatural.

Emma seems to concentrate a bit more to read minds. She has these intent stares. Maybe for her it's the reverse: that reading minds is rather like closing one's eyes and concentrating and her default state might be "switched off" to telepathic input?