I would imagine the reason why manufacturers stopped using RF remote controls is because of their size. In order to control things via RF, you must modulate and amplify the signal. Also, the more functions needed within the remote, the more complicated the circuit will get. For real world examples, think of the remote control for a RC Plane or Car, and then the control for remote keyless entry. These are all examples of RF remotes. Infared on the other hand, can be controlled by either using different wavelengths of light, or pulsing the signal (digital signal). These things are much less complicated, with less chance for error, with the only disadvantage being line of sight.