No no no! They didn't say Windows was the only vendor, but replacing Windows with another OS (Linux in this case) isn't feasible.
The cost to renew a contract with Microsoft is only the cost of the contract, the cost to change to Linux would be way higher, since you have to replace your whole application platform, teach the users how to use Linux and all the new apps, teach the techies the ins and outs of Linux etc. etc. etc.
This isn't so easy as just installing a new operation system and be done with it. That's why Windows is currently the only solution until they get the money to replace the whole platform. But try to explain that to the Bundesrat (the federal council of Switzerland) and the swiss parliament.
And btw, if you are Swiss and it means so much to you, you can always start an initiative, but I want to see how you explain the higher cost to the swiss people and why they sould bother.
In the end the Swiss government is right: At the moment there is no competitor, as bad as it is, and they won't be able to explain to anybody (except geeks of course) why they should spend so much more money. In the end I'm sure you could save money, but try to explain that to people who first plan to build two tunnels through the same mountain and in the middle decide to abandon one because "it's too expensive" (they soon *have* to finish the second one because traffic is so bad, but now it will cost way more).