I think this subject has been discussed many times, especially for '00', The response from manufactures was that omitting the motor had very little impact on the final cost of the model. A case in point being the Heljan 00 scale class 25, the 'ETHEL' version without motor is the same RRP as the motorized version.
I do agree however, if priced right then I would buy locos without motors for double heading or for additional locos for standing in a depot.