5CC is becoming too easy

At the release of Alara reborn (early May 2009) I was thinking that maybe non-basic lands are getting too powerful, and mana-fixing too efficient. Alara Reborn gave us the trilands...See, the point is that when you use more than one colours, you're taking a chance. You have to sacrifice constistency for power Using more colours gives you more possibilities - see, instead of having to use the enchantment destruction of, white you can use the slightly better one of green.

With all these dual doublelands - it's becoming even easier to play 5CC, as it's called, the decks with all five colors. Now, take a look at the new double lands for the M10 core set

Given you already control one of lands of a friendly color-pair, this kind of dual land will produce both types of mana. It is not a first turn-land, meaning it is kind of balanced. It simply gives you better choice for the next turn.

But I wonder, why are these new duals rare? Is it because they're so good, so strong? So by putting them in the rare slot, their power will be limited? If they are so strong, they should never have been printed. Moneyspending and serious players will get four of these even though they are rare. If they were common - they would deplete basic lands.

On the other hand, there won't be more than four of any of these in a deck. Maybe it is just good for the game, making it easier to taste the colour cake.