Excellent point, real skill can be demonstrated without the need to strike your student hard. I would say it takes more skill to chi-sau hard and then stop at the point of impact. Emin tends to just bash his students when in chi-sau, just brute force.
If you look at this clip on part 3.26, you will see chi sau done hard, but with no strikes to the students. From Leo Au Yeung, a clear demonstration of skill and technique without the need to hurt the student.
http://www.youtube.com/watch?v=NvGuaTk4B38