Geography could be an influential factor, but it's not the main reason. Christianity as a faith/religion started there and expanded. However, the details regarding slaughter were not taken over by Christian practitioners. Therefore, I assume that slaughtering practices, although have a ground on religious doctrine, are merely preserved though traditions. To exemplify, I'll give you the following situation: strict Judaism (Kite, correct me if I'm wrong) strictly limits travel during Sabbath. Highly religious Jews even count the number of steps they take. However, the Tanakh, which is canon, does not specify that travel should be limited. It says that a man should avoid doing unnecessary work. I can provide other examples from Islam too (traditions), but I'll stop here, for the sake of the ones reading.
3c...I agree that it's a horrific death; but; I wanted to know the background of this particular practice!