The Ethernet Connection has many advantages over USB. It is more reliable as Ethernet runs a client-server connection, while USB runs as a Windows Device. If there happens to be any glitch in the communication, you can lose the USB device and it would need to restart it to re-establish the connection. Ethernet can reconnect and establish the connection on the fly.
USB requires sharing of the grounds. This is something that you want to stay away from, especially on larger machines or plasmas. There are lots of voltages and EMI noise. All those cables for connecting devices are acting as antennas bringing them back to the electronics. You do not want to send all that to the ground of your PC. The Ethernet connection is capacitive, it does not share the grounds. It is designed to interconnect large networks while not sharing the grounds or creating ground loops on the wiring. This can save you a lot of headaches.