PH,
I suspect the reason the most hunters call the Brown Bear "Coastal Grizzlies" are because they are wanting to make sure the distinction is clear between Black Bears (and their various color phases) and the Brownies. I've seen a lot of print about "Cinnamon" Bears, while most know these Cinnamon's to be Black Bears, it does confuse some. So for full impact, most will call the Brownies "Coastal" Grizzlies. Which they are a subspecies.

Also, for a lot of years, at least here in Alaska, Boone & Crockett and the Safari Club, kept moving the line where one was either considered a Grizzly or Brown Bear. I recall the line being 50 miles, 100 miles, the arc of the Alaska Range, and a few others.