Yes, you're absolutely right, it could just be that I was unlucky and got a 2nd MacBook Pro with the same hardware defect as the 1st; after all, mine was of the 1st produced & the second was probably of the same build (I doubt they'd have changed the designs by then & I suspect lots of people who experience new this with those earlier machines either don't notice or put up with it if they do.
I would like to experiment with a new machine to test that theory but I don't have the option unless I buy another, and do the testing within the return window. my issue there would be that if the new one proved perfect - I would have to convince Apple to refund the existing on to make it equivalent to a replacement, something I don't think they would entertain.