That is all great except that you have to know:
1. What an invulnerable save is described in the main rules and where it is located.
If you look at the original he and his friend just started playing Dark Eldar. Perhaps they did not know where the information was located?
In this game the information is in a confusing array of books. Perhaps you know all that information because you have a lot of experience playing this game AND finding that information in all of those books. Perhaps this person did not. He was asking for an answer, it was not a substitution. What this forum gave him was "read the dang book"
I just do not understand how answering someone, directing them to the correct books, and generally being friendly hurts this forum, YOU or anyone else.
If that same question had been asked in person would you have given the same answer.
I think not. The internet tends to make people much more crass then they would be if they were standing in front of you.