It is a pretty standard layout, just less common.
It was a very common layout at one time; in the early days of 101-key keyboards, except for the Model M itself, about the only company that made the other layout, the same one as IBM had, was Keytronics.
However, that just makes it a pretty common layout; it is still not standard at all. The keyboard IBM made was the standard for the IBM PC, and other manufacturers simply had the choice of being compliant with the 101-key standard, or being non-compliant, by making a keyboard similar to the 101-key keyboard, but with the main typing area modelled after the 84-key standard keyboard.
Standard, of course, isn't always good. Thus, Keytronics made a nice nonstandard keyboard with 10 function keys that was roughly similar to the 101-key keyboard before IBM had the idea.