I'm pretty sure all of the ocean that surrounds Northrend is called the Frozen Sea, not just to the north. It's kind of arbitrary since it all connects into the Great Sea anyway, but I don't think it's technically wrong.

The REAL game breaker is that once you're on the Skybreaker, they go on about how we need to go at full speed to catch Deathwing before he gets away. Then, right on queue, our good buddy Warmaster Blackhorn and his friends proceed to pewpew the engines... Now, one would thing damaged engines would not work so well (or at all), and with everyone then focusing on making sure Blackhorn doesn't cause the airship to EXPLODE, one would think Deathwing would have ample opportunity to get a nice lead ahead of the airship. Yet, once Blackhorn is killed, everyone is simply able to jump out the bottom of the airship and right onto Deathwing's back. What'd he do? Say "Gee, with this plate on my back missing, I might get a sunburn! I better keep that airship above me to protect me from the sun's harmful rays"?