Dan Dare,
I cannot under any circumstance refuse someone a clearance through Class D airspace because there RT is not up to scratch, it is quite frankly more than my job is worth. I can refuse because the zone is to busy etc but not because someone isn't to hot with the radio.
Do you get treated differently , how can i treat you differently as I said, the only thing we do is issue very specific instructions and possibly keep an extra eye on them , that is human nature.
As for ATCOs saying those things about GA I would hope they are firmly in the minority, however some units are not there to provide certain air traffic services and will possibly only provide the bare minimum such as an alerting service. Each unit is funded differently and some do not get paid to offer a service to GA.