Edit: I forgot that the ’13 RT isn’t a wethead. It is the wethead version that had the licence code and limitied number of activations. Sorry for any confusion.
I guess they ran out of the first batch. I finally got mine (for the GS, it is the same DVD) a while back after many months of waiting. FWIW the current version of the DVD comes with a license code. The code allows the product to be installed 3 times if my memory is correct. After that the DVD is mostly useless. If someone does offer you a used DVD make sure that there are still license activations available.