There are also reasons they stopped using it in the first place[1]:
Some problems with this method were that the receiver could be triggered accidentally by naturally occurring noises, and some people could hear the piercing ultrasonic signals. There was an incident in which a toy xylophone changed the channels on such sets because some of the overtones from the xylophone matched the remote's ultrasonic frequency.
While each specific problem could be worked around with modern methods, it looks like a technique reserved for situations where you don't have a better option.
I don't see why DTMF https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_sign... couldn't have solved this pretty easily without adding too much complexity. I've seen those remotes before and they usually only had about three buttons on them. Still pointless, but I think this would have worked.
Some problems with this method were that the receiver could be triggered accidentally by naturally occurring noises, and some people could hear the piercing ultrasonic signals. There was an incident in which a toy xylophone changed the channels on such sets because some of the overtones from the xylophone matched the remote's ultrasonic frequency.
While each specific problem could be worked around with modern methods, it looks like a technique reserved for situations where you don't have a better option.
[1] http://en.wikipedia.org/wiki/Remote_control#Television_remot...