It probably won't surprise you that I'm not on Valve's side regarding this whole "disabling Thai copies". (Although forcing you to play a Thai copy IN THAI instead of in English might be fair.)
Different prices in different countries are something that we all live with. But y'know? I can order clothes from Canada and have them shipped here. I have to pay import duties, but I am allowed to do that. Nobody sets my clothes on fire because I bought them in a different region.
I can go to Vermont and come back bringing maple syrup that was a lot cheaper than it is here. I can go to India and bring back spices. I will have to clear customs with these goods and possibly pay some tax. That's why customs EXISTS. Because importing stuff is LEGAL.
Watch the news - with currency fluctuating people happily take big Shopping Vacations to different countries and load up on goods that are cheaper there than at home!
So why is it fair to apply different standards to software? It isn't, obviously. It's just that they CAN (until/unless someone sues otherwise) and therefore WILL. That's capitalism - if you CAN make an extra buck, you're an idiot not to.
And this, friends, is why I do not buy games that I know can be remotely enabled/disabled by a distant company if they choose to try and extort me.
Do I think Valve are evil? No. I think they think it makes perfect sense, and that people should buy the local copies, and they feel hurt that you're trying to 'screw' them by buying the cheaper ones. They're just not realising that the world doesn't revolve around them.