Let's make something clear:
The best thing to do for a North American who wants to drive overseas (Europe, Africa, Asia, Australia) is to fly over to either Australia and buy a Land Cruiser diesel (and then ship it) or UK and buy a Defender.
Both models are plentiful and cheap in these countries.
In both countries you can register/insurance the vehicle without being a resident.
But that does not work well in the real world for several reasons - people are not well informed, they don't want to deal with the paperwork or they prefer to have the vehicle at home beforehand to get it ready.
That being said, there are excellent vehicle options available here that would get you through 99% of the situation and will allow you to drive everywhere.
Chris S. and Tom are without doubt experts but don't forget that there are thousands of other people driving all over the continents with all sort of vehicles.
I have myself seen VW buses, 2CV, Mitsubishi vans, Ford F350, Iveco, Nissan Frontier, even 2 Trabant...the list is endless.
We have to be extra careful not to give an impression that you must have a Defender or else you better stay home. That is ridiculous.
Parts availability is always a risk no matter what you are driving.
In Ethiopia I was traveling with a German guy with a newish BMW R1200GS. His rear bearing gave up and he had to have one shipped to Addis Adaba. It is not the best situation but it can be done - the worst that could happen is that you are going to be waiting for a while and pay extra duties.
100 Series Land Cruiser are a perfect example of a car that is available here and is seen all over the world - even in the gas version and with IFS.
I have seen the petrol version everywhere, from Cape Town to Syria.
Yes it would be nicer to have a diesel but a lot of people prefer the gas version as it gives them more power when driving in sand.
I have also met a guy personally whose transmission gave up in Mozambique and ended up having to tow the truck back to Johannesburg - and he had a diesel.
(you can read the whole story here, it's pretty funny)
http://www.greenafrican.com/?p=333
So there is no guarantee either way.
Like everything else in life, it's all a matter of balance and calculated risk vs cost.
So to get back to my original point, I say we have more choices here than we are lead to believe.