Not sure...Might be true for good developed countries, but what about Bolivia, Venezuela, Pakistan etc? Touring isn't that popular world wide as it's quite expensive and time-consuming entertainment.

Ok, this is an old topic but I'll answer anyway.

Sorry for my english!

So, in 2011 I had a long trip from Texas (USA) to Ushuaia (Argentina). It took 6 months. I had a very simple bicycle which I got from REI. The bike was equipped with 700C wheels.
What I learned from that journey: NEVER EVER use 700c for international trips! It was a pain in the ass!
I was able to get to Guatemala, then I stuck there for 2 weeks waiting for 700c tires an tubes I ordered from USA because the local stores did not have 700c! Next stop was Buenos Aires (Argentina), same problem!

All America outside of USA has no clue about 700c! Probably Asia too.

My advice: use only 26" to be able to change your tubes and tires in every bike shop!