You really do have to admire those guys for their effort and for doing it on bikes that are so old.
I've given some thought to the idea of a world tour on one of these:

It's a civilian version of the Diesel KLR 650 that the US military is using.
I don't think that it is in production yet, the projected cost is around 15K.
Which is alot for a bike of this type, but then it gets 100+ mpg (which would make up some of the cost).
With that kind of mpg's if you carry two 5 gal Jerry cans you have a range of 1500 miles.
Add a Daylong saddle and I think it just might be the perfect bike for an adventure tour around the world.