WANTED: Feather reciever
Receivers that we use now with the closer channel spacing need to be more "selective" which is a term in electronics which has to do with the receivers ability to receive the signal on the channel it is set up for but to reject the signals close by on adjacent channels.
To do this most effectively, most manufacturers use what is known as a dual conversion design in their receiver. It has to do with how many times the signal is converted to another frequency while being processed by the receiver's circuits. (JR uses a different approach with their ABC&W receivers)
Basically, a single conversion can meet our narrow band specs but it can't reject unwanted signals nearly as well as the dual conversion can. If you fly at a club field, there is a risk of being "hit" by another transmitter especially if it is on the channel next to yours.
I know there are others that could tell you more but I hope you get the basic idea here.
Tony