Just from informal observations, I'd guess that at least 15% of the vehicles you see in the Highlands are old Land Rovers - mainly Series III and Defender SUVs and pickup models.
So why all the old Landies? After chatting with some locals I found out why there are so many. The vast majority are used for "farm vehicles" in the tea and produce plantations. The Malaysian Armed Forces wear them out and then sell them to the public... mostly to farmers and adventure tour companies. The trucks are narrow and perform well in the rough, muddy, and often rocky terrain.
The older Rovers we saw would often have a large "CH" painted on the doors indicating they are only for farm use. Their owners can provide limited, lowcost insurance if the old trucks are only used for local "farm to town" purposes. The Tanah Rata tourist board estimates there are approximately 4,000 Land Rovers in the Cameron Highlands region alone. In 2009, local Highland farmers held a harvest parade. The parade contained over 400 farm-based Land Rovers as part of the procession!