That is the thing with contracts.
If you sign up to a contract, and dont abide by the terms of the contract then it cannot be discriminatory.
I would hazard a guess that you must be present at a garage to sign off the handover and due diligence.
As always, there are rules to handover a £30,000 vehicle and to make sure it is done safely and correctly.
If you cannot meet the requirements of the contract why sign up for it in first instance?
Motability do give quite a bit of latitude in their business, and there is prbably more to this than meets the eye.