Russ, though I agree that your math is correct and your logic too, I think the equation is more complicated than that.
When you compare the cost of the oil to the purchase price plus the cost of gas, the oil is a small part of that equation.
The other thing is we want to keep our engines running as close to new as possible, with like new hp and like new smooth feel & sound. That's always more important than how many miles the next owner can run the engine.
Then there is the "Do I realy own this!" factor. Lets say you always wanted car X, but it is just out of the question for your wife, so you just concede to the situtation. One day the two of you are relaxing on the patio with your mom, and your wife brings up the fact that your best friend just got an X with all the options, making fun of the way you drooled all it. Mom responds, "Why don't you just get one then if it's what you realy want." You just smile...
The next morning your wifes says: "So are you going to get that X today like your Mom said?" You say: "sure, I'll pick one up on the way home, luv ya." She says: "Wait, your Mom is right, if that's what you want, go get one." So you decide to think it over a bit and get on your way to work.
At work you mention this conversation to the guys who respond by asking assuming questions like what color, and when are you going to get this X?
Later in the day, the guy with the new X, (which has more opions than you would ever consider,)joins you for a short break and says I have good news and bad news. First I just got the promotion of my dreams, big raise and bonus. "Sounds great, what could the bad news be?" He says: "My first assignment is two years in Europe. I'll have to sell the X, and you know I'll take a beating on it."
Three weeks later you Mon is bragging about her son who still is smart enough to follow her advise and your wife is consistently asking if she can drive the X today. You answer yes most of the time, but today you say: "sorry, I need to change the oil today."
Now, which oil you going to choose? Keep in mind that the answer has little to do with either math or logic, and more to do with preserving.