I know several professors in graduate degrees for engineering, chemistry, physics, etc. that explicitly do NOT hand out A's for their classes.
For example, I never had an undergraduate course at my university where no student scored an "A". I had a professor for one of my chemistry graduate classes that refused to give an "A" grade to anyone. Not on the basis of student performance, but based on his policy.
I do agree that the overall GPA should generally be higher than undergrad., but its not always as easy as it seems!
SMPs are great and everything, but in terms of difficultly, some masters are just as hard/harder.
For example, if the OP went through the Maters degree I went through, then it would be impossible for him to retain a 4.0 GPA. Those were not handed out in the MS chemistry program I had.
Plenty of 3.5-3.9 though.
I also feel like a high grade in something like "Advanced quantum chemistry 600" should remedy some errors in undergrad. courses like physics 100 or chemistry 100.