I have seen more than a few threads on this topic over the years with people saying that dive guides have no responsibility for their safety. The people writing this have always been non-professionals reporting their beliefs. In those threads I have seen several divemasters and dive shop operators write that in their experience, the dive guides are absolutely, positively expected to provide that assistance.
Then there is the question of what would happen in the courts. As an instructor, I was very clearly told that if I was in any way acting as a professional such that a diver believed he or she could depend on me, I could be held liable in an accident. This would obviously be true if I were accepting payment, but I was clearly told that if I even said something that implied that the diver could depend on me because of my status, I could be liable.