A HI is not an electrical professional. There may be some that are very good with electrical knowledge, there may be some that only know what they have been taught to look for, and if they see something they have never seen before they will balk as they have no idea what they have or if it is safe. The good HI will mention such items that they maybe have no clue on and then suggest an electrical professional be consulted to further analyze that situation. Any disagreement with the HI findings should probably go to a professional in whatever area is involved to further analyze the situation. If the HI found a structural problem or a plumbing problem that sounds a little "fishy" then a structural expert or a plumber should be consulted to further figure out if there really is a problem.
As has been mentioned if there is just one or two GFCI's in question, maybe he did find a problem even if it is a fairly minor problem and you just change them and be done with it. If all of them are questionable - then maybe there is a need to find out if he is correct with his interpretation of the problem, I sure don't want to replace all of them and find out they still respond in similar fashion to the originals.