Actually, there can be other reasons too. I run a car on a company car allowance scheme, which requires my car to be of a particular size. I can only keep it until it is 3 years old. Under the terms of that agreement, the 2006 Mondeo I have now has cost me a considerable sum of money over the term. My calculations suggest that the Epica I currently have on order won't cost me anything.
Yes, the depreciation in percentage terms is much worse for the Chevrolet, but in terms of hard cash the differential is much less than you'd think and perhaps in the Chevrolet's favour. Chevrolet also offer a 3 year servicing package for £449; I reckon that my outgoing Mondeo has cost me £1400 plus over the last 3 years.
I have tried other similarly priced cars, and you should be wary of lumping them together - this is a significantly better car than the Chrysler Sebring, for instance, which might look better (arguably) but which rides and drives like a tractor with the sound insulation missing.
Is the Epica better than my Mondeo? Probably not in a brisk drive around corners, but on a lazy drive down the M6 on a busy Friday evening? Well, the toys suggest it will be and I can tell you now that in that queue the handling will count for nothing.
And besides, I have a classic TVR in my garage for when I want to do the corners thing. The difference in price between the Ford and the Chevvy will cover the running costs of that with some considerable ease for years to come.
So before you dismiss the Chevvy driver as an idiot, consider that their circumstances might be different to yours.