I had that same perception. While it was more easy to find low quality 26"x1.75" tires/rims in Russia or southeast Asia, this wasn't as big a deal for me for several reasons:

-- high quality tires seem to last for a long time, e.g. schwalbe marathons lasted half way across EurAsia, and folding versions of these aren't too heavy to carry along
-- good bike shops found in largest cities did carry 700c
-- I'm heavy enough that if my rims go, I'll want a good quality rim again

If I can easily pick, I'd go with 26" for third world touring, but that isn't as strong a preference as it used to be for me.