Oh I understand just fine. If you're so close to the edge of your budget that 10% extra depreciation, amortized over several years, will ruin you, for a supercar, then you're doing some poor life choices
No, you're still not understanding, probably deliberately since I know you're not stupid.
Firstly, the difference may well be much more than 10%. If you compare the 720 with the 765, for example, a 720 is going to depreciate at around 50% over 3 or 4 years, and a 765 might not be depreciated at all, or maybe 10%. This makes the total cost of ownership of a 720 far greater than a 765, so from a purely monetary viewpoint, it's much cheaper to own a 765, although you may or may not have the cash flow to actually afford one.
Secondly, that total cost of ownership then factors in to the purchase of the next car. After 3 years, there will be far more equity in a 765 than in a 720, making the next purchase much more affordable. This is exactly why residual value is important to the manufacturer because it directly affects the potential sale of the next new car.
In the case of the original question on this thread, comparing a 750 to a 765, it's a very relevant question since the gap between the two cars is relatively small. 750 a bit softer, greater range of performance, 765 arguably better looking, more raw, maybe a bit quicker. It's all marginal stuff, but there might potentially be a difference of $100k or more total cost of ownership of the two cars over 2 or 3 years.