Sony equipment use to have a way of doing this as well, via the S-Link[1] / Control-A1 bus on stereo equipment (and some video equipment too, I believe). There's a handy Arduino library[2] for doing this - a couple of years ago I added support for the dual cassette deck I have, although the PR hasn't been merged yet. I'd also be remiss if I didn't mention the Slink-e [3], a commercial product that seemed to be very capable (unfortunately it is now discontinued).
In fact, these protocols are (I believe) more capable than a regular "Remote" socket since they allow bi-directional communication, meaning you can both send commands to the equipment and request data from them. But it's been a while since I've looked at them in detail.
Also, I recall being confused by the several (seemingly incompatible) systems offered by Sony: S-Link, Control-A1 and Control-A1 II.
[1] http://www.brian-patti.com/s-link/