Land Rover's research has shown the 100" is the optimal wheel base for off road work. Hence the Defenders sitting 10" either side of that golden mark and the Rangie sitting right on it. Land Rover even experimented with a military 100" Land Rover (Series - Defender) 20+ years ago.
I would say my Classic Rangie is as capable off road as my Defender in its standard setting. I've got slightly taller tyres on the RR, which is a help, the only times it's ever been stuck is when the wheel ruts have been deeper than the clearance in a bog hole where I haven't been able to see where to place the wheels.
The Defender is an easier vehicle to live with in the bush as far as cargo loading goes, and that may be one reason Defenders get to go further. My current Defender has taller tyres than my Rangie, Difflocks all around, 2" lift... So it's the vehicle of choice for 4WDing for me. However my SIII which had a weaker engine and less articulation than the Range Rover, although being less capable off road than the Rangie (except for ground clearance) was still an easier vehicle to live with in the bush for extended periods.
Or... Maybe it's just got to do with the calibre of Defender drivers ;)
