90% of an RJ45 jack is mechanical. Assuming that the body is still billet aluminum, they could have milled the clip part into the body very easily. And nothing about the jack itself needs any cooling/airflow. The only electronic parts that need to be near the jack are some simple passive electronic components.

Note that if this was any other company, I wouldn't even begin to make that argument. However, I hold Apple to an admittedly higher standard, and it's not as if many, if any, components they use are off-the-shelf anyway.