Well, it's sort of serious. A lot of people seem to think that "Professional" implies something about the target market that means the computer should be upgrad

Well, it's sort of serious. A lot of people seem to think that "Professional" implies something about the target market that means the computer should be upgradeable/have a firewire port/use compact flash/sport a replaceable battery/etc. But it could actually imply exactly what the word suggests, and yet still mean none of this. In actual fact, of course, it implies nothing, and that's why it means none of the above. "Pro" is just a badge, as meaningless as the "Sport" that adorns my car (4 doors, diesel engine).