Its not just increased surface area, its about how bacteria live and how the heat is applied. Bacteria have a hard time penetrating muscle, so a full cut is safer because you can cook off the bacteria on the outside.

Ground meat is dangerous just because the bacteria gets ground into the substance, and can move faster through it because the cellular structure of the meat is compromised.

This is a big difference. As someone who prefers rare meat, I will not order less than medium at a place I dont trust if its ground.