I really don't see what that has to do with Microsoft. 7-zip is GPL and cross platform. In fact - I just checked - a command line 7-zip is available by default on my Linux Mint install.
Right, but an xz-supporting compression tool is shipped with many Linux distros, whereas you do need to grab a tool to support xz on any version of Windows.
But you're right, 7z is an under-appreciated format.
