"I suspect the same would be true for Microsoft or anybody else as well. If all Microsoft did was make their own distribution of Linux or UNIX, people would likely say they too didn't write their own operating system."
Almost certainly, though I'd imagine it would be that with the amount of closed-source code MS would stuff into "MS Linux" distro, the Linux people would be throwing a fit. I mean, just look how many people consider Nvidia to be evil for tainting the kernel with their closed-source video drivers.
"It might have to do with the fact that instead of porting their software to work natively on Windows, they force it to work through a slow, bloated API wrapper."
Agreed, and they cant be bothered to write a native Windows application for reasons above.
I was just pulling that Next stuff off the top of my head, I couldnt remember whether Jobs founded it or was simply there was the early inklings of OSX were developed, but I was certain they laid the groundwork for Apple's OS, and since most people think Jobs=Apple, it really does mean that they developed their own OS, unless we want to claim, like you said, that any variation on Unix is not really new.
Besides, the same people complain that Windows has become such a bloated kludge, that should we even be proud that MS *did* create their OS from the ground up?
Probably should have headed to Wikipedia first about the Next history, but oh well.