[Melas]

But even he could drive his wheelchair off of a cliff if he wanted to

That's something of a stretch don't you think? Given that he requires 24 hour care, I think Hawking would find it difficult to find himself at the precipice of a cliff, able to wheel off without at least one other person complicit in the attempt.

[chimera]

He'd certainly need transport to a suitable site, maybe someone to set up a ramp, but from what I saw on that one program he is still capable of controlling the device, so the ultimate act could be initiated by himself.

Which seems to be the whole point of this "assisted" suicide business, isn't it? Get someone else to be responsible for "pulling the trigger"? As I alluded to earlier, that seems a bit cowardly. Just "do it yourself" if that's what you really, really want to do. Leave others out of it. Again, I don't advocate doing that, but it seems like a valid argument against the "I need someone else to do me" cop-out.