"f I need to buy a specific piece of proprietary software to submit my tax information online or if all applications for public sector jobs are distributed in the latest MS Word format that I can't open without buying a new version of Windows and office then that is something I at least potentially care about."
Thats the point of this Microsofts lobbying, lock-in. Can you today require open documents from your government? Here in Sweden, no. You get .doc most of the time, if it is a local government then perhaps a PDF.
For the most part you can, sometimes you will get a .doc it's almost always available in another format or it's an old enough .doc format that opening it is not an issue.
You can also grab lots of data from parliament in XML format and people have done some cool things with it (http://www.theyworkforyou.com/) for example.
There's lots of government depts that can be interacted with using various XML formats and they will provide you with all the schemas you need.
Thats the point of this Microsofts lobbying, lock-in. Can you today require open documents from your government? Here in Sweden, no. You get .doc most of the time, if it is a local government then perhaps a PDF.