"There’s some truth to that, because Apple decided not to leap into a completely new system but instead to evolve the existing one."
That's not really true. What they decided to do was build copious backwards compatibility with OS 9 into what was essentially NeXTStep and then re-skin the OS so it looked Mac-like. All the backwards compatibility stuff was essentially new, I believe, and not ports of the OS 9 internals.
You can maybe squint at that quote and say it's not really false, but it certainly doesn't get it right at the technology level.
I think it comes down to, which matters? I wrote code for OS 9 (via PowerMops, of all things), and for OS X (I shipped two major Cocoa apps), so I'll vouch for the fact that you are technically 100% correct. On the other hand, what became OS X had a radically different design than Rhapsody: even comparing OS X 10.0 to OS X 1.2, the former could run apps natively that could also run on OS 9, the former could read HFS+ filesystems, the former had apps like QuickTime, the former ran Classic apps that couldn't legitimately run natively right alongside the newer Cocoa/Carbon apps, the former had legacy APIs like OpenTransport that the latter lacked. You can argue, correctly, that, technically, OS X is more NeXTSTEP than Mac OS. But I'll give Isaacson some space. His misunderstanding is well within the bounds of what I experienced within the non-Apple programming community at the time. I'd cut him some slack.
"His misunderstanding is well within the bounds of what I experienced within the non-Apple programming community at the time."
Yeah, but you didn't have access to Steve Jobs. And Isaacson probably could have also talked to Bud Tribble, Avie Tevanian, Ali Ozer, etc.
Frankly, I'm not even sure why anyone would expect Gates to have any particular authoritative insight into OS X. Microsoft's concerns would have largely involved the effort of porting Internet Explorer and Office from Mac OS to OS X. Anything new in OS X that didn't require changes in their software could be ignored.
That's not really true. What they decided to do was build copious backwards compatibility with OS 9 into what was essentially NeXTStep and then re-skin the OS so it looked Mac-like. All the backwards compatibility stuff was essentially new, I believe, and not ports of the OS 9 internals.
You can maybe squint at that quote and say it's not really false, but it certainly doesn't get it right at the technology level.