Don't agree with the guy really. He finished the game on Insane and was disappointed by the fact that he didin't get anything special?
Well, yes, it would have been nice, but there are not that many people who will do that, a tiny percentage of the total number. Developers are reluctant to spend time on something that a tiny number of people will see. It is a shame, but if you are going to do that, it is better to go the whole hog and do the Dead Rising type thing.
I am currently working through the game on Insane and loving it, as he said, but thats the main appeal to me. It is fun. And, if I do it all, I get an achievement. No big deal, but nice to acknowledge what you have done.