Well, I'm pretty sure all the money of those companies would not be enough to get LibreOffice to become 100% compliant with MS Office formats in a timely manner. Those formats represent decades of features, bugs, fixes and quirks that would have to be replicated in order to make sure that LibreOffice can replace MS Office in all its uses.
Let's assume it costs $5/month per instance of Office 2000-Whatever. It's really more than that with the MS ASP licensing, but let's use $5 for round number sake. Let's also assume they have 500K users using Office, also what I would consider a conservative number.
That's $2.5 Million/month in licensing costs alone. That pays for quite a bit of developer time.
The real question is, could Office be cloned for less than the user cost of Office? It almost certainly can't be cloned for less than Microsoft's cost to make Office.
