I see that the XBee-Pro ZB has a 2-mile range (under the MOST optimal LOS conditions, I'm sure - but a good spec noetheless) and is on a through-hole PBC.
Do you have a link to this XBee with through hole PCB? Most XBees (all that I've ever seen) have a bunch of pins with non-standard spacing (at least non-breadboard standard) and no through holes.
Obviously this is no issue for the plane's receiver but I'm wondering if that's just because the system is made to accommodate the proximity to the motor or if it's simply not an issue?
If the motors do not affect the receiver, it is not because the receiver is immune to noise. It is because the motors have capacitors to absorb the noise.