Because when you connect it to Ubuntu, it sees iPod touch as a usb device and I think it allows to format it also. So, I wonder what would happen if I format my iPod Touch?
iOS doesn't expose a "real" filesystem over USB. On my work Windows PC (without iTunes installed), one can see only the photos, and Windows recognizes it as a camera. (Also, it won't let you format it.)
So, since it's a fake filesystem, it probably won't accept the formatting commands.
If you try it, please tell us what happened!