Actually it was a "preorder" deal, but just not in a separate case. There are two different versions of MK DD out, only the preorders were suppose to come with the bonus disc, the regular versions were to be on the store shelves and the one stocked after the preorder deal had passed. Of course depending on the number of preorders, and how the store orders, and how clueless the clerks are at the store you shop in, you may be able to find the preorder version for sale. I've heard some people getting all pissy after they paid for preorders and then went to pick up and received regular editions, or had to bitch at the sales people for giving out the wrong one.
But the special preorder versions are marked on the front, just have to shop arround if you want one, as some stores might still have extra preorder versions forsale.