Their old car doesn't get downgraded components or fuel, nor does it drive any differently on the road.
PS4 will get "significant" downgraded games.
If the suspension, engine & gear train are based on newer versions there will be a significant difference in driving experience & possibly even longevity of the vehicle.
What about the interior? The new model could have sat Nav & a minibar built in.
The best thing about your backfiring metaphor is that your first paragraph is true of the PS4 - it'll still play PS4 games, which will look and perform like PS4 games.
I'm taking the sacrifices comment to be relative to the PS4K output, rather than worse performance in comparison to existing PS4 titles.