If all you have to do is dash out a quick Word document or put together a simple Excel spreadsheet, then yes, any basic knockoff program will do. As in the example for my client I mentioned above.
But the business world works with Microsoft Office for the most part, and one of the biggest reasons for that is because other programs integrate with Office products (especially Word and Outlook).
I'm all for marching to the beat of a different drummer, but saying there is no reason to thoroughly know Office if you are working behind a desk is simply ignoring the reality of the workplace. The moment one needs to work with irregular formatting, margins, paging, watermarks, password protection, etc. etc. one will quickly wish they had spent some time with Word first. More to the point, Word itself has changed dramatically over the last three iterations.