Well, some companies are writing more in roman letters e.g. Shell Thailand where the main and other headings are in roman letters. Others are writing more in Thai letters e.g. เมอร์เซเดส-เบนซ์ ประเทศไทย (Mercedes-Benz) where even the html page title is in Thai . May be this is just pure chance or tells something about how much you care about visitors of your web presentation or about your customers in general.
In the near future even the URLs can be in Thai. Why is this introduced? I think people prefer their mother language even if they are able to talk and write in a foreign language.