Katie I'm assuming the access/gateway/opening to the drive is difficult, there is more room once inside. Perhaps the gate is on the edge of marryj's property and her front garden is on the other side, so once the car has got through the narrow bit, there is room to get out, open the garden-side doors to unload (and also the boot).
Maybe the neighbours do have an issue with the drive-parking neighbours, they just haven't posted it on mumsnet; maybe they've had issues but marryj doesn't know about it.
I think it's rude and entitled to decide on someone else's behalf that you can park across their drive. The drive is there for a reason, it doesn't matter how often it's used, it's someone's drive.
It's a bit like the sort of wanker who blocks someone in, when parked on a road, because they'll only be an hour or so, or because the car they're blocking in has been there a week and not moved.
Er, hello? Do you see the wheels attached to the vehicle? Do you know what that means? It means it moves - therefore it might actually need to move, and not at a time convenient to the entitled twat who has decided their need to park without consideration overrides someone else's need to move their car. [bit of a rant there about parking in my street but the principle's the same]