It's a very interesting question and quiet valid curiosity and concern.
Based on my few car ownership, I can share my experience and reasoning to best of my thinking and hope that satisfy your curiosity.
Range Rover: Super comfortable, that I have never driven that level of comfortable car / suv yet. First time my wife sat in it and reacted this car has cotton wheels or it's flying above the tarmac. I know it's EAS (electronic Air Suspension) is awesome, but there a lot of other things, engineering and efforts required to achieve that level of comfort from seats, chassis balancing, engine and other component weight distribution, viewing angles, ergonomic cabin design to reach almost everything within one hand reach, very high quality and durable stuff used (leather, plastic, rubber, door seals, sound proofing etc.)
Mercedes ML 500: Not as comfy Range rover for sure, but cabin inside is extremely beautiful and elegant to keep the Mercedes standard alive. Meticulously crafted details from leather finishes, stitches, bezels, dials, etc is just too pretty and inviting you to stay inside as long as you need. Instead of being 5.0 NA engine still it gave awesome fuel mileage than all my other full size SUV's I have owned. That's engineering marvel and it cost big money on R&D any day.
Porsche Cayenne Turbo: Slightly uncomfortable, due to more sporty suspension and cornering ability but amazing accurately response to transfer 3 ton metal into a beast when need arise with a just a tad harder push of a gas pedal. I was totally impressive with Porsche engineering more than anything else. Designing engine, gearbox, 4x4, and torque management band were just absolute brilliant that comes with endless hours of research, patience, knowledge and practice. All this cost a fortune to perfect every mili-second delay or cornering perfection at over 100 kmph without skidding the 3 ton beast.
In a nut shell, what I feel that every premium luxury car has something or the other thing to offer as per your taste as a main component (USP) and then followed by overall higher grade of material used, hand crafted (in some cases), carefully appointed sound system, head lights and tail lights and with endless introduction of newer technology.