Edit – was writing what Jérôme just explained.

I heard a comment that a particular instructor will not utilize sign offs.  If that is the case perhaps not the best instructor for a given individual.  Choose another instructor who will offer sign offs appropriate to skill level.  Personally I agree with the concept of sign offs.  As a helicopter CFI it was up to me when to solo a student.  Some were skilled and safe at 8 hours.  Others at 20 hours.  Overall it sounds like a disagreement with an instructor, not a reason to change safety rules.  If a student has not been given a sign off it may be that his instructor is erring on the side of safety until the student has shown more improvement.