I believe pretty much every Fortune 500 company has mission critical applications running on...Microsoft Excel and VBA. There is no way this is going to be displaced in the enterprise, when you have so much legacy code, macros written in VBA (and not simple ones, I'm talking incredibly complex ones with tons of business logic), people have all the keyboard shortcuts memorized, etc. There is a huge huge huge amount of stickiness here, and that's why people have not switched to the free StarOffice, etc.
Probably less of a pain to switch from Word, but the pain to switch from Excel and Access is horrendous. I have written quite a few of these programs for several different jobs at different companies, so I know that switching to something "free" has a lot of cost. So, the moat may continue for another 10-20 years simply due to the legacy/switching costs.
On the other hand, for those small businesses just starting out without legacy code, the free tools are quite attractive.