Well Adam,
I have not seen this month's comic so am going on what you have posted, for reason 1, that Kent is too far away........? Too far from where. I am from Kent and brought a WW2 British lorry along, as I always do, there were a good few British softskins around, perhaps the mag writer did not venture around the fields to see them or they were so well camouflaged ;-) To be honest, I can think of quite a number of vehicles in this catagory, in this area of Kent, Sussex, Surrey, which do not attend for one reason or another, but there are just as many postwar owners who also do not go there with their vehicles, many owners just prefer to visit the show and views others and go around the stalls looking for that illusive part. I do not fully believe that it is because the owners are now getting on, because some of these are owned by younger people who prefer to collect vehicles from our own countries military history.
It could be true that some vehicles are going overseas and can think of a very few, but not significant numbers. I just looked through the programme and in the medium class, there are 18 15cwt trucks listed, a fair percentage being Bedford MW, also Morris C8 gun tractors, Matadors, Scammells, Austin K2, K3, K6, Bedford QL, OY, Fordson WOT models, and WOA2, Tillies.
Not sure whether a WW2 British truck is an investment though, the prices have stayed reasonablly level for years, unless you see one for sale that has had a lot of money spent on its restoration.