Actually if the ice was as thick as some said it was, the lake should have handled this weight rather easily. Of course we should all know that ice does not form nor maintain the same thickness everywhere. Pressure ridges, insulating snow, air/gas pockets all need to be accounted for. Clearly this fellow got a long way out on the water before hitting a problem (remember the horide series Ice Road Truckers?? that carried 100 tons of materials to the north slope??)
If you want a good dose of education on weight carrying capacities on typical ice go here >>>
http://lakeice.squarespace.com/bearing-strength/
If things go wrong, even a plow truck can be too much. Ice kills more sledders each year than any other hazard out there.
Never assume you can get over it without stopping to think if the ice gives way what you are going to do. Unexpected break-thru and lack of preparations is what mostly takes a life. There is no such thing as completely safe ice either. Today it is good, and tomorrow it won't hold a man on foot.
