I've lived in Thailand for 14 years, in Bangkok and now Pak Chong, and speak to Thais everyday. I studied Thai at AUA and then with a private tutor. But that's just my anecdotal experience.

I gave two references to standard Thai, a dictionary and a video teaching basic Thai by native Thai speakers. Both show the Thai words for "yes" and "no". If you have an reference of any kind that indicates there are no words for "yes" and "no" in the Thai language please link to it.