Just semantics
The IMA motor/generator (aka "electric machine) is of a type most commonly called "brushless dc", but in an academic taxonomy of electric machines, this type would more properly be categorized as a permanent-magnet synchronous ac machine. So you are both right--it's a floor wax and a dessert topping!
Why this confusion? Well, the dc in a dc motor is really just in the wires coming out of it. The current in the windings inside the rotor is actually switched by the commutator brushes, and since it is switched to go one way, and then switched to go the other way, the rotor-winding current is actually ac. In a brushless dc motor, the commutation function (swapping current directions) is performed by semiconductor switches (e.g. MOSFETs). and the windings are on the stator instead of the rotor, so that there is no need for brushes to connect current to the rotor (which instead has only permanent magnets). So now there is DC coming to the MOSFETs, but then switched ac current going from the MOSFETs to the windings. That three-phase cable is between the MOSFETs and the windings.
So there really is ac in the wires going into the motor, and hence it "properly" should be called an ac machine. But for historical reasons, and because of the conceptual similarity to dc motors, it's called a dc brushless motor.
If you go buy something called a brushless dc motor, and something else called a permanent magnet (PM) ac synchronous motor, they won't be quite the same, because the brushless dc motor will (hopefully) be optimized for square switched waveforms whereas the PM ac synchronous motor should be optimized for sinusoidal waveforms. But that's a minor difference--either one could run on square or sinusoidal waveforms.
Charlie
ps--this is being discussed simultaneously in this thread:
http://www.insightcentral.net/forum/vie ... php?t=3080