Most of us need a car. None of us need rMBPs and could get by just fine with a cheaper laptop. Also, car loans can be had for under 3% APR if you shop around and have good credit, whereas most credit cards are in the double digits for APR. IMO it's okay to finance a deprecating asset like a car if the APR is low enough and the necessity is high enough. But the rMBP is a toy that can only be financed at an outrageous interest rate.
Oh, and the Apple/Barclay's card with 0% interest for 12 months? Read the fine print. You get 0% interest if you make all your payments on time and pay off the entire balance by the end of the 12 month period. If, when making your last payment at the end of the promotional period, you screw up, hit the wrong key on the keyboard, and pay all but one remaining cent of your balance, they will go back and charge you interest for the entire purchase amount for all 12 months, at a 22.99% APR.
So how many of you people using the 0% interest offer were planning on paying most, but not all of your rMBP off in 12 months and thought you'd only be paying interest on a couple hundred dollars balance if you dragged it out to 14 or 15 months? That credit card statement on the 13th month is going to look pretty ugly.