There's no question that MS has engaged in anticompetitive practises with regards file compatibility to push general office programs from Lotus, Corel and others out. Armies of lawyers on standby to defend. But ultimately, MS Office now ends up on most systems, because of Outlook, it's Calendar functionality, and the Active Directory being considered near de-facto requirements.
AD is popular with businesses because of the concept of centralised administration for thousands of users. Unixland it's obviously possible, but not really standardised or wysiwigged to the point where you can give the config tools to a monkey to drive (and still get it wrong, but that's a different point).
In my experience the compatibility breaks between spreadsheets opened on different systems come when you start doing graphical stuff; stuff that can't really be standardised implementations. Or anything involving macros, obviously. The latter capability is, regrettably, rather useful in Excel, for all of my preference for Open systems in just about every other case.
There are plenty of fringe, specialised tools with advantages and disadvantages e.g. SPSS is pretty good at cobbling up statistics from datasets. Excel can do it, but requires more effort to achieve what it SPSS considers a standard outputs.
Biting the hand that feeds IT
