2. All those platforms have supported mutually compatible formats for as long as that has been relevant (that is, after some standardization on network hardware). That local variants stems from different OS's having different features that need support. E.g., Windows' complex ACLs vs. POSIX permissions (support for ACLs on UNIX-like platforms came later).
3. Office for Mac was a product developed by an entirely different team, having no relation to the regular office products. It's natural it was not identical. However, the solution here is not to force Microsoft to make 1:1 products for all platforms. It's to let alternatives grow: No one needs nor wants Microsoft Remote Desktop for Linux. We have FreeRDP, Remmina, and others. Don't monopolize computing.
4. You can either try to hide an OS and inevitably favor one over another (thereby significantly crippling the others), or you can expose everything (which usually leads to complaints about how much work it is for the developer).
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1. http://www.os2museum.com/wp/why-does-windows-really-use-back...
2. https://en.wikipedia.org/wiki/Model_F_keyboard#/media/File:I...