Doesn't an apostrophe s signify ownership of something? Is a master's degree a degree belonging to a master? And what about masters' degrees? I vote for no punctuation.
Actually, yes it does mean a degree pertaining to mastery of some subject. Think about the other interpretation. Is it reasonable to think of masters degree as a plural?
I agree. They aren't proper possessives. You can say the hat of the man (man's hat) but you can't say the degree of the batchelor or the master - without meaning something different.