Not sure if you have to buy this game 2 times as I think it is only the beta which is currently available to pay and play.

But this looks this is an offer for the 'finished' product to be released at a later date.

See here:

http://www.minecraft.net/prepurchase.jsp

By looks of it, you get the game now, and a free copy to give out to someone else as well.

So 2 copies for 15 euro