I understand now. The Sony cable isn't HDMI. I looked up the PS3 connections (video link
here), and there is a separate A/V output jack that is a rectangular connection.
So - those Sony cables aren't HDMI-to-analog. Whew. The world makes sense to me again.
EDIT: On the other side of this, though, the reviews did say that the Sony aftermarket A/V cable performs quite a bit better than the standard cable that comes with the PS3. So, it might give acceptable performance.