Why Wi-Fi gaining over RJ45
The speed of data transfer on a wired connection depends on Cable, Connector and the Crimping. Ethernet over Coax (EoC) co-axial cable. Optical and Gigabit Ethernet over Optic Fibers. Copper twisted pair and others are other means of Digital Data Transfer over Ethernet.
Wi-Fi and WiMax helps freeing the user from wires. Remember Wired is more secure than Wireless.