When you purchased your XDJ-RX, you bought a stand-alone device which is capable of playing rekordbox prepared content. Nowhere on the packaging or product description was there mention of being able to control rekordbox as a DVS directly from the controller. There is absolutely no reason for you to be upset right now, no matter how much you paid. Your RX already does more now than it was capable of at the first release.
What I can tell you is the initial rekordbox DJ release will only support certain models of the Pioneer product line, but that will be expanded to include other models as time goes on. You can continue to use rekordbox (even rekordbox 4.0) as a tool to prepare and link your content to the RX.
Patience is your friend.