Well, this is going to sound racist, but it's not. It's just an observation I've made in my 20 years of living in my home town. El Paso has a predominantly Hispanic population (
proof), and as a result, there are fewer causasian people here than in other cities, I am guessing. What I've noticed is that this "Saturdee" (or "Mondee", "Tuesdee", "Wednesdee", etc. for that matter) pronunciation is almost exclusive to causasians, at least in El Paso, but there are a few exceptions. I'm not claiming that this is a universal truth; I'm just saying it just happens to be somewhat true in El Paso. I have yet to hear anyone say "Sar'dee" here though.