[Mondial]

Using a cathode bypass cap on the output tube was an engineering design decision, not necessarily dependent on the cost of the extra part. 

Including the cap increases the voltage gain of the output stage at the expense of added distortion. Eliminating the cap has the effect of providing negative feedback, thereby reducing distortion. In this case, the loss of gain must be made up elsewhere in the audio section, otherwise the radio will not play as loud as it otherwise would.