Excel also has a deliberate bug where it thinks 1900 is a leap year because they wanted compatibility with Lotus 123, where the bug was actually a bug! [0]
Reading Joel’s post again, I suspect Bill’s style of review (having read the spec, made notes, and having a “F” counter for screwups) lends credence to the idea that he would have done exactly as Joel did and sought out Fries or some other senior Excel person if he didn’t get a satisfactory answer.
As Joel laments, you can’t bullshit a programmer, and Gates was (underneath it all) a programmer.
[0] https://youtu.be/bC6tngl0PTI?t=325