It also has a lower heating value. And the faux pas is really that the stroke of an internal combustion engine controls the compression ratio only if the combustion chamber volume is held constant. I don't actually know the answer to bamdam's question, but what I do know is the limits of my knowledge. The reason is that the CI engine cannot burn the same quantity of fuel that the SI engine can. The result is that the piston will have moved considerably away from TDC while the injection proceeds, and less expansion is available to the burnt gases.
Compression ratio is determined by the swept volume and the unswept volume.
Diesel engines are unthrottled, which means no suction throttling losses. Diesel has a cetane rating, gasoline an octane rating. The two rarely correspond. Go back and read Greg's message. Greg is correct is his statement, did not really intend to be a blanket statement, but thats what came out.