Every now and then -- ok, every 2-3 posts -- someone will point out how 26" tires are more widely available than 700c, and are thus preferable for touring outside the US.
So, I'm curious as to whether this is actually worth worrying about. As someone who hasn't spent 2 months cycling through Chile or Tanzania (yet), it seems like you'd be more than set with 2 spare folding tires, spare spokes and 2-4 tubes. (Assuming you start out the extended tour with new tubes and tires.)
Am I right, or are there really places where you can end up destroying tires on a regular basis -- and replace them with tour-worthy tires -- in the middle of nowhere?
From personal experience in some long tours, I've changed my mind on this over time.
In 1992, I crossed the US with 700c wheels. I had two folding spare Michelin tires and at least three tubes. As luck would have it, I lost one tire to a cut on the first day and the second one crossing the continental divide on MacDonald pass coming into Helena. It was a Sunday arrival into Helena and bike shops were closed. I hurridly had my parents express mail another folding tire to Miles City. I had some other tire issues later in that trip, so if you asked me in 1992, I would say getting a common tire size is a good thing.
In 1997, I crossed Canada with 700c wheels. This time I thought I'd get the tire issue licked by taking three folding tires. This time my problem was that I cracked three back rims. The first time this happened was at the Laird River at mile 500 of the Alaska Highway. A combination of weekend and the Victoria Day holiday meant I waited six days before a bike shop was able to build another rim and send it up via bus. Tires weren't as bad of an issue as rims. So, if you asked me in 1997, I would say that spare tires are frequently common and the issue might be rims or other components.
In 2001, I bicycled one lap around the outside of Australia. This time, I thought I'd get the rim issue licked by switching to 48-spoke rims with a Phil Woods hub. The rims generally lasted well, though around 10,000 mile mark near Broome in Western Australia, I noticed stress cracks appearing in the rear rim. Better safe than sorry, I had the bike shop in Broome replace the wheel with a new 36-spoke 700c rim. (I had a spare 48-spoke wheel back in the US, but shipping costs would be high). This meant waiting four days while a wheel was built up in Perth and shipped up. Unfortunately for me, the bike shop put in a wheel with improper spacing and forced open my aluminum frame. Further unfortunately, I didn't notice. Hence, 1000 miles later my frame cracked. At this point, I flew back to the US and picked up a new bike including a 48-spoke rim to continue the trip. So, if you asked me in 2001, I would say that even spare rims or tires might not do it. In total, I went through ~10 tires over 17,700 miles and had a preference for Continental Top Touring since the Michelin ones seemed to have gone out of manufacturing.
In 2007, I bicycled across Russia. This time, I thought I'd get the bicycle issue licked by switching to a steel frame and also leaving behind a "spare bicycle" in Russia on a previous trip. By now, I was using Schwalbe Marathon XR tires. These worked great. One front tire made it all the way across, a total of 8000 miles. I replaced my rear tire once at ~4000 miles and this one was well worn when I made it across. I did lose one rim near Lake Baikal. However, my brother was visiting during the trip and he brought a spare rim that came right in time.
So, now if you ask me... I think the quality of touring tires has improved and I'm a strong advocate of Schwalbe tires. Except for the most extreme, I wouldn't necessarily switch to 26" wheels just because of tires and would rely on good quality folding tires. In the most extreme cases it would be costly but DHL or other package suppliers could get you tires most places around the world. Rims are still an issue for me. While a local 26" rim might be more common, I'll still have issues with durability and hence I solve that in a different manner by getting the best rims possible and working things out if problems appear.
Bruce Gordon Ti Rock N Road , Fat Chance Mountain Tandem 
MEV: Your experience mirrors my own.
I have been using 700cX45 tires for over twenty years on mostly off road tours from Alaska through South America without the <dreaded tire problems> feared as often expected in these forums. Try to remember that before mountain bikes arrived people toured the same world on 700c or 27 inch or 650B rims and tires.
My choice of quality tires from Ritchey long ago and in recent times Schwalbe Marathon XR have proven quite successful for me. My only rim problems has been the side rim surface wearing thin eventually. Again high quality rims do make a big difference in my experience. This is from a Clydesdale rider too using 36 hole rims.
Tire pressure, weight carried and riding style can enhance the longevity of wheel components or cut them short. Over the years my equipment load has shrunk and I rarely have any bike equipment problems even on a rigorous rough route like the Divide Ride.