My point is you wouldn't actually 'feel' it, therefore you wouldn't get back the 'sensation' of touching something. Yes you would _see_ a response, but you would not _feel_ the response. Ergo, illusion.

EDIT: For your enjoyment, http://en.wikipedia.org/wiki/Ultrasonic_sensor, you simply do not feel ultrasonic sound waves.

The distinction seems a little iffy, but I can see how there's a difference between the sensation of touch and the illusion of touch. You get the illusion because you're expecting to feel the sensation of touch and you feel something, however if you were to really sit there and analyze what you're feeling you'd realise that it isn't quite the same as the actual touch sensation.

It's like the old ice-cigarette trick -- you pretend you're going to burn someone on the back of the neck with a cigarette, but instead you touch them with a piece of ice. They'll get the illusion of heat from the actual sensation of cold, because... well, our brains are dumb sometimes.