FTA: Apple also added Enter to the numeric keypad, although an Enter that almost exclusively did the same thing as Return.
If applications followed the UI guidelines, Enter behaved like Return if enter didn’t make sense in the context and vice versa. Yes, that was mostly (when do you have UI to enter a multi-line text to be processed as a separate unit?) but when it mattered, return started a new line, and enter sent entered text to be processed by the application.
MPW shell was a (?the?) prime example. In its editor, Return started a new line, Enter executed the current selection or, if there was none, line.
No, it works like that on mine. How amazing that I never noticed!
The habit of using Enter has been so ingrained for so many years that I never tried pressing Return before now. Has that always worked? I suspect that it didn’t at some point in the past, though it may be you have to go back a long way. Or perhaps I've been mistaken about this for decades and never realised…
On at least some Macs well into the 2000s, I remember that if you had a dialog with a text field in it, Return would add a new line in the text field, but Enter would _always_ choose the button with the thick black bar around it (typically "OK"). There were also some websites where OmniWeb (remember OmniWeb?) would interpret the Enter key (but not Return) as "click the 'next' link on this page", which was great for paging through webcomic archives and the like.
If applications followed the UI guidelines, Enter behaved like Return if enter didn’t make sense in the context and vice versa. Yes, that was mostly (when do you have UI to enter a multi-line text to be processed as a separate unit?) but when it mattered, return started a new line, and enter sent entered text to be processed by the application.
MPW shell was a (?the?) prime example. In its editor, Return started a new line, Enter executed the current selection or, if there was none, line.