As others have mentioned this all has to do with a probability of overstay. Somebody who's independently wealthy in a foreign country is going to generally have strong ties to that nation as well as property and other things that tie him to that nation. Poorer individuals have fewer ties and are going to be statistically more likely to overstay.

The individual from this blog has no employer, is a Thai national that writes more fluently in english than most natives, is carrying out part of his 'bucket list' -- traveling the world, writing about it on a personal page that's been mentioned by sites such as the BBC, and providing video including time lapse/high framerate footage shot from high definition AV equipment. There's an extremely high probability that he's rather well to do.

I'm guessing that being Muslim might have had something to do with it. I'm sorry they couldn't join you regardless.

It is in general very difficult for people from developing countries to get tourist visas for the US, including majority Christian countries.

The religion of the country makes a difference? Wow.

Huh? That’s not what I said.

What does the comment about ‘majority Christian countries’ mean?

I said "including" not "especially" or "exclusively".