As you say "Microsoft doesn't bother writing" and his girlfriend uses MS Word on OS X if I understood. Can she then use that feature to recover her work after she had done the "Save" from the MS Word or not?
No, she's probably not going to be able to recover her lost work. What OP and others are trying to point out is that OS X has support for saving revisions to documents if application developers (like Microsoft) would just take advantage of it.