The CDJ / DJM setup (eg. the Nexus2 system) is primarily designed and marketed as a stand-alone DJ solution. In this scenario, rekordbox is used to organize and prepare your music, as well as optionally link to the players over ethernet. While they have the capability, the objective is not for this system to be used primarily as a controller for rekordbox DJ; we have several other dedicated solutions in that category. The DJM-450 and DJM-900NXS2 are targeted at two very different market segments and as such, the decision has been made to include a rekordbox DJ license for this entry-level product.
Thanks for your feedback.