Scott,
my VA 7 has the same kind of Eq; when I increase its frequency at a given value only a narrow zone around that value is affected. You can check that by yourself: if you raise your low Eq at -say- 120 Hz, if you were raising ALL the frequency below that one you will hear the bass drum jump out of the speakers (like in techno music). To get that effect, you need to center the Eq around 50 Hz. Similarly, when you raise your high frequency around 3000 Hz, if you were raising ALL the frequencies above that one you should be able to hear a well definite hiss. In my VA 7 neither of these things happens, so I think that just a narrow zone around the chosen frequency is affected.
Since in these keyboards the equalizer is nothing more than a welcome plus, I think that Yamaha can be justified for not clarifying its specs more in depth.
Regards,
Andrea