I feel that the parking fee should also be waived for guests with disabilities. We stay onsite and prefer not to have a car, but we often travel with my MIL, who uses an
ECV, so we rent a van when she is with us. It's MUCH easier to get around WDW with a van when you're dealing with an ECV than it is to get on and off buses, to the point that we don't even consider NOT renting a vehicle - it's just automatic. Now WDW is going to tax us $20/night essentially because of a disability? That's insane.
Fortunately for us, we're in the process of purchasing DVC resale, so we'll be staying on points from now on and won't have to pay the fee (assuming the free parking "perk" is extended to those who purchase resale). But the principle is the same - they shouldn't "tax" disabled guests who have little or no choice about using a vehicle!