I don't understand all of the complaining about Mewtwo. Let's put it this way:
Which would you prefer?
Mewtwo only being available to those who buy both versions (which might not even be the situation we are in),
Mewtwo not existing?
I think the answer is obvious. There is absolutely nothing wrong with companies rewarding their customers for supporting them well.
Assuming Mewtwo doesn't get release in any way shape or form if you don't buy both versions, how is ignoring more than half of your fanbase a good thing? What about the millions (literally) of gamers who decide to buy only one version?
The problem is not Mewtwo existing or not, the problem is how you have to get him.
You're looking at this the wrong way. Mewtwo is nothing more than a thank you bonus. He's not an essential part of the game. If you only buy one version, whichever one it is, you will have a blast regardless. Making Mewtwo only available to those who buy both does not take away from those who only buy one.
Unless you are either, 1- A hardcore Pokemon fan or 2- A massive Mewtwo fan in Melee, it's a pretty shitty thank you reward if you ask me, you are basically paying $100 (assuming you bought both games at full price) for a single character. It would be better to call this a 'bonus' (a small one at that) rather than a 'thank you' reward.
I go into the second group, that's why this pisses me off so much, since I simple won't buy Smash Bros. for 3DS.