Though MM may in fact use *nix solutions as stated, I find the opening line of that post is disingenuous as worded, so I've edited it here to make it more obvious what is being said:
No open source software that I've seen handles the Microsoft proprietary format docx halfway as well as the Microsoft native applications for the format, Word 2007 and Word 2010.
Bolding mine, to point out the obvious deficiencies of that argument.
I agree that your alteration makes his point clearer (although I'm unsure it was really necessary), but I'm not sure it's as much to the argument's detriment as you think. I'm probably going to come off as a Microsoft fanboy here, but so be it.
The reminder must be made that companies both create a legacy of existing files, and must use files by other companies. If you were to flick a magic switch, today, and have all your users understand a new suite of office applications and religiously save into an open format, you would in no way have solved your problems. Their blissful glee at being able to do what they were already doing but in a slightly different way would last until the moment they tried to open an existing file, or one from an external source, that "doesn't look right". And yes, I know I'm going over the same old points that get made, but I'd argue that 1) they're unfortunately still relevant, and 2) with respect, your own points aren't new either.
One additional aspect that usually gets skipped over is Microsoft Access. Yes yes, toy database, shouldn't be used in business etc etc, but we all know it does. I don't believe, and please correct me if I'm wrong because I haven't checked in a year or two, that any of the open source suites can attempt to open .mdb files. There are now open source Access-like systems to create databases, but again, what do you do about the legacy information? With databases, it's even more likely that these may be currently used, critical files.
As you've said, the starting point is probably to begin using the open document formats in Microsoft products, until all the documents made with older formats are simply not relevant anymore; for my part, our company has only migrated a few users to a version of Office new enough to *have* those formats, so I'm stuck with .doc whether I like it or not. In the end though, it's rather amusing to consider that if, one day, we find ourselves in a situation where the majority of files are created in an open format and switching to an open office suite is easy, it's likely because Microsoft bridged the gap this way.