You wanna know how such an ingame cinematic comes to light?
Here is how:
Imagine this conversation between Blizzard CEO JAB, Bobby Kottick, Danuser and Ion Hazzikostas:
Q: How do we stretch a lousy xpac through 3 major patches, story wise?
A: We swing from cliffhanger to cliffhanger, like Tarzan.
Q: Investment?
A: Cheap!
Perfect! Make it so!
PS: When you look at the quality of WoW and other Blizz games these days, you understand that above meeting was declared as a whole work day. After such a hard and long meeting, they mostly gonna drink some whisky and play golf, to relax from all that hard work.