When cars like the Duesenberg SJ roamed the streets, luxury cars offered things not available to plebeian Ford Model As. Lots of power, supercharged dual overhead cam engines, decent brakes, high end paint and trim.
These days, there aren't many features offered on high end cars that aren't offered on even basic rides. The Focus can park itself, high end stereos are available in pretty much anything, automatic climate control, etc. The only thing that distinguished many luxury cars from plebeian rides is they offer more or marginally better versions of the same features. Even there, you can get a 500+hp Mustang for far less than the equivalent AMG super coupe.
I think it's easy for middle range or low end brands to legitimately claim at least a piece of the luxury market because the delineations are nowhere near as clear as they once were.
As far as Rollers, they were made from top notch materials, but were hopelessly outdated in their engineering and miserable to keep, you know, rolling. Now that they are just upscale versions of BMWs, they are much better.