It is possible to get a PPL at a non radio field. Would you be happy about such a person entering a busy radio driven airport. A lot of controlled fields do have a lot of traffic and snappy concise radio is the core of smart handling in such environments.
There is a minimum standard for RT and this is monitored by the issue of the FRTOL.
Having said that given the number of people who er... their way though clearances you would not believe such a licence exists.
How bad could it be if such a standard does not exist. Believe me you would happily pay £35 for everyone else to be as good as you.