Bang & Olufsen fixed this years ago...
I used to work in hi-fi retail and apart from all the UK and Far Eastern mainstream kit, we also sold a LOT of B&O.
B&O used a 7-pin DIN connection between their receivers, turntables cassette decks and eventually CD players. And the B&O remote controls would:
a) Allow you to press one button, lets say Preset 1 of the radio, which would power up the receiver and it would start playing at the preset "switch on volume".
If you then fancied listening to a CD, (and the disc was already inside) just pressing "CD" on the remote would switch inputs and play the CD. If you then wanted to record the CD, (and a blank tape was inside the cassette deck) you just hit the "Record" switch.
Once you were done, and you wanted to listen to an LP, (and a record was on the deck) pressing "Phono" would start the turntable, stop the CD player and stop the cassette deck. Pressing the "power" switch would then switch EVERYTHING off with just one button !
And if you had a B&O system compatible with the B&O Master Control Link system, you could do this from another room !!
Some other manufacturers did something similar, BUT it was only on a simple mini or rack system and was not fully implemented across their entire range of products (whereas the B&O Remote protocols was).
it does seem rather strange that in the computer world, once PC's became dominant, you could pretty mix and match components from multiple vendors (HDDs, CDROMs, keyboards, mouses, VGA cards, monitors, ISA or EISA soundcards and/or memory cards, etc etc) and yet for audio and AV systems, this is virtually impossible, which has lead to the situation the OP mentions - a plethora of remote control devices. You'd have thought a common standard would have been adopted years ago... :-(
And there's also the inevitable problem of a remote working, just as it's batteries then drop below the working voltage threshold and you cannot then turn the device off by remote and then you can't find any spare batteries !!