Legroom They need the car for rear space. Legroom in the back. No other car offers it. Nothing - not a Skoda Superb (more legroom), a S Class SWB (more legroom), I could go on... no. Range Rover is the only car which offers legroom. Oh and don't forget - their DH is tall, so what else can he drive?
As I've said upthread, the legroom is crap in the back of the RR Sport and better in our Ford Focus/Seat Leon. The interior fittings are bulky and the front seats are high so it's quite claustrophobic in the back. Add in a tall front seat passenger and it's even worse.
Size It has a big boot. Again, no other car (Superb, S Max, Passat estate, Alhambra, Sharan) exists. No other car can do what the Range Rover can in terms of load space. Quoting statistics is irrelevant - Range Rover is the 'biggest'
The boot isn't that great either, my Volvo XC90 had a much bigger and more usuable boot.
I bought mine as I liked the look, it was really smooth to drive (and quick acceleration which can be useful in heavy traffic on roundabouts etc) and I thought the level of interior finish was beautiful. My replacement BMW is also nice but a step down (bar the reliability).