It Is Sort Of True
If you are entering Thailand without any type of Visa it is true. If you fly in most countries get a month, but if you enter overland it is only 2 weeks. We crossed over from Malaysia about 6 weeks ago and it was the easiest border crossing of our trip to date. While in KL we picked up a 2 month tourist visa, and Thailand gave us one month on the bikes. They would not budge on giving us more. They just told us to to go to another border crossing and get it extended. And they did. We went to customs in Prachuap and they extended it the extra month without any questions (or fees!).
We also went before the first month was up and they still extended it one month from the old expiry date, and not one month from when we asked. We leave in 2 weeks, so lets see if that extension holds up when we go to leave. (There is no reason to think otherwise, Im just paranoid the first time I do these things!)