That blog post you keep linking to has nothing to do with region locking, it is for what happens after you log in to your account. You must buy from the correct region, or you'll be locked out on launch.
Trust me or not, but you're wrong here and you will be annoyed by it on launch.
Basically, you can play on whatever server you like with whatever region copy of the game you've bought but crucially, you can only login and play using a US copy of the game if you are in fact logging in from the US or logging in with a EU region copy in the EU otherwise you will be locked out of the game at launch as Wakers said. It's to stop people from buying the game at cheaper currency conversions.
In short, I wouldn't bother, you'll be disappointed and sorry you didn't pay them properly.