Standard,Genuine Heavy Duty Shocks??

I've noticed for the first time that there appears to be a genuine (standard) Land Rover heavy duty rear shock absorber for Defender 110s & 130s.

What are the advantages of this over the "normal duty" genuine rear shock absorbers? Is the difference in ride quality or durability?

I assume only the rear comes in heavy duty because of weight expectations?

Can anyone shed light on this? Yeah... a lot of questions...

Valving and resistance to heat during use affecting them, like oil v gas dampers at a guess