If he was only 50 feet from the dock, he may have been "speeding". The following is an excerpt from the Safe Boating Guide.
Shore-line speed restrictions
Certain provinces have adopted a province-wide restriction to limit speed to 10 km/h within 30 metres from shore on all waters within their boundaries, except for:
waterskiing, where the vessel follows a trajectory perpendicular to the shore; or
in rivers of less than 100 m in width, or canals or buoyed channels; or
in waters where another speed is prescribed under these or other regulations.
This limit is not posted. These restrictions apply in the provinces of Alberta, Manitoba, Saskatchewan, Ontario and British Columbia (Inland waters only).
As far as comparing this to an automobile collission. A diver is more akin to someone out running (or jogging) at night, clad all in black, and running across an intersection in a non residential area, not like a kid running across the street in front of his house in the middle of the afternoon. While you might have been on a crosswalk and have the right of way, after the police look at what you were wearing and lighting, as long as it doesn;t appear the the driver was speeding or failed to stop for a red light, etc, the odds are real good that the driver will not be charged.
I don't want to sound unsympathetic to the victim here. We dove Big Bay Point on July 1 and noted a lot of boat traffic. I still can't figure why so many of them run so close to shore (maybe they figure they can swim to shore if something happens the boat). Noted the same thing yesterday at Cedar Hill. Why, in a bay that's miles wide at that point, would you run up the shore less than 500 feet off the beach? Maybe it's the same reason PWC's (jetskis, etc) need to play close to beaches and swimming areas. They need an audience. Hey, look at me, I've got a boat, see how fast I can go, see how big, white, shiny it is. What they really should get is a LIFE!!
When we entered/exited at Big Bay we nearly crawled along the bottom until we were well along the dock and right beside it before surfacing. And we nearly got jumped on by a couple of kids jumping/swimming off the dock.