This sounds like received wisdom. Is there any evidence to support it? Why would one believe that a land rover's engine requires more maintenance than the average engine found in all the aggregate "old trucks"?
The reason I made my original statement is that old, frequently ex-military trucks and old busses form the backbone of a lot of central and northern africa's transport networks, and the local mechanics are incredibly ingenious and experienced at performing "bush repairs" or fabricating spares to keep them going.
https://en.m.wikipedia.org/wiki/Toyota_War
https://en.m.wikipedia.org/wiki/Technical_(vehicle)
http://www.newsweek.com/why-rebel-groups-love-toyota-hilux-7...
The more correct way of characterising both would be that they will continue to run and function without ongoing maintenance (the proper level of which is way above a modern vehicle) until they break in a spectacular and often terminal way.
To attempt to answer your question, I think the general implication is that "old trucks" are designed for high maintenance intervals whereas Land Rovers, especially as used by the military, are designed to perform a function for short intervals with the long-term aid of a logistics chain.
One bloke had his Citroen die in such a way in Africa... and had to rebuild it into a motorcycle to get out of where he was
http://www.dailymail.co.uk/news/article-2168061/French-elect...
https://m.thevintagenews.com/2016/05/18/emile-leray-built-wo...
I find this fascinating. To a layperson like me all combustion engines seem like they must be uniform. Thanks.
I have a 2001 Nissan Xterra that's been sitting in my driveway for almost 4 years with a blown head gasket because of the combination of lack of spare time, other available vehicles that I could drive, and the complexity of disassembling the engine to remove the heads. The seats and hatch area are now full of engine parts and I still have to finish taking off the passenger side head.
Contrast that with my 1987 Toyota pickup: I would have had the entire job done in a weekend with time to spare.