The receiver packs for four AA batteries come with basic radio gear - because that radio gear could be used for any number of uses and its a way to power the receiver.
Nitro use a receiver pack, as do some electric classes that either use too few cells such as 12th on-road, and things like dragsters running many cells - where the ESC either doesn't have the ability to power the reciever at all, or would put out too many volts.
You'll almost never see a receiver pack in a 10th off roader. just cast it aside!
