why can’t they implement SSE3 by other, more powerful instrutions (like AVX)

In short, the instruction semantics are slightly different, so they don’t do exactly the same thing. But it’s likely that the execution unit hardware is re-used for those.

…and the cycle repeats:

1. Threat: Apple generates a lot of interest in ARM CPUs
2. Response: Microsoft goes all in with supporting ARM on Windows
3. Fail: Windows’ greatest asset is their backwards compatibility, and people just want to be able to run their programs. ARM doesn’t have the same level of compatibility as x86, generating little interest amongst users to switch, due to the risk factor
4. Undo: fortunately, in this case, they probably don’t need to really undo much, it just ends up being wasted effort

(personally I have my doubts whether WoA will succeed; maybe it will, but I couldn’t resist adopting his own hype into his own model of failure)

To see what ATTO is writing to the file, we wait until it has completed a write pass, and then cut power to the machine.

I question how reliable this actually is. It might be fine, but I could see it not working as expected (e.g. OS didn’t flush all writes, or reverted something when rolling back the filesystem journal etc).
Regardless, one would think that intercepting the WriteFile call and examining the buffer would be more reliable (or strip the FILE_FLAG_DELETE_ON_CLOSE flag when opening the file).