I don't think the maths was wrong, just the assumptions were possibly optimistic. A $1500 car doesn't really depreciate much (unless it dies), but a $12000 car

I don't think the maths was wrong, just the assumptions were possibly optimistic. A $1500 car doesn't really depreciate much (unless it dies), but a $12000 car does. And then there's the 12% investment return figure. (Still - the overall point is very valid)