I believe Guinness has always had a lager in their portfolio. As a matter of fact, Revvy posted a Guinness ad from years ago advertising it. Not sure if it was ever available here.
Zixxer, the BJCP disagrees with your opinion, considering Guinness Draught (and canned), is the first example listed for the Dry Stout category. Guinness Draught is the reason you won't find too many craft examples of regular dry stout. They can't compete, and its not worth trying.