There is crossover between Thai/Lao/Khmer but if you are somewhat familiar with Thai script then it's reasonably obvious that many of the letters are different (like you can see that Cryllic (e.g. Russian) script differs from Roman (e.g. English).
My impression is that a lot of the "magical" stuff in Thailand dates from Khmer empire days (see some of the links I gave), hence the Khmer script. Theravada Buddhism a later overlay...