In a first-season episode of the US TV show Kitchen Nightmares, the well-known chef Gordon Ramsay states that there's a "big difference [in] taste and flavor" between Maine lobsters and Canadian lobsters. He gets into an argument about it with a restaurant owner who claims that they're really no different. (If you're in the US, there's free video of the argument in question here, from hulu; start at about 16:33.)
Admittedly, I don't know whether Maine lobstering waters and Canadian lobstering waters border each other, though Maine waters and Canadian waters certainly do. And Gordon Ramsay owns more Michelin stars than I own plates, so he's clearly the expert. But I also find it hard to dismiss the owner's points — if they're true — that both lobster types are the same species (Homarus americanus), and come from the same North Atlantic waters.
So, what is the cause of the difference in taste/flavor/quality between Maine lobsters and Canadian lobsters?