how do I know that I shouldn't buy this MW2 product from anywhere I want in the world ?
Common sense indicates that you shouldn't buy "discount" games from shady looking sites. Barring common sense, there's the Steam ToS.
I have the right to buy from anywhere in the world that I want
You don't, actually. It's against the service provider's rules, and they have the right to deny service to anyone who breaks the rules.
my dad often buys stuff for his boat in many countries because it's simply not distributed everywhere, how is that wrong ?
That's a little bit different from paying for a service at another country's price, despite it being available right where you live, simply because it's cheaper there.
ho and France companies/industries are already blamed by some people because they buy in china, move their production to china & the like, yet they still do it because it's cheaper for them. now we users wouldn't get the right to buy from the same china ? how weird is that ?
This isn't a fair 1:1 comparison here. You could certainly move your computer to China, buy your keys there, activate them there, and play your games there. If you think all that is worth saving $30 per game.
unfortunately this logic is a bit flawed, there is people who can afford and others who can't afford in every country.
Half-price keys were meant for people who
live in a region where generally they couldn't afford anything more. Not for you.
Better?
Activision isn't doing this out of the goodness of their heart because the poor people of china earn less
I never said it was out of charity. But the relative incomes of each region *does* have everything to do with the pricing.
really it's all strategic,
Yes, it's their strategy, it's their right to use whatever strategy they like to maximize their profits (barring illegal strategies), and it isn't your right to play games with this strategy. They make cheap copies available in China so that they can sell some copies there. Not so that you can save a buck.