@David *********
nope, It's NOT and the immigration people at the government complex wouldn't know even if it was a rule.
That's because tourist visas are sold by the thai consulates which are run by the Ministry of Foreign Affairs, NOT by the immigration office which is run by the Royal Thai Police.
I can assure you any place you find a time limit about how long you can stay in thailand on visa exempt entries or tourist visas it's someone quoting that rescinded rule I mentioned before.