The reason for the recommendation is that the Mixtrack Pro is widely considered the ideal starter controller, just look at the poll results for the “What do you think is the best Entry Level Controller?” thread in this forum for an example. The jogwheels on the Numark controllers are really nice and are a good size.
Also, with so many people using them there are a ton of different mappings available so it’s pretty easy to get it set up in a way that suits you. The other bonus for the Mixtrack Pro is that in addition to the normal bundled software (Traktor LE or Virtual DJ LE, depending on where you are) it’ll also run Serato DJ Intro which is quite nice (and has fantastic cogwheel response with the Mixtrack Pro).