If they're able to calculate the TCO difference, they most certainly had the numbers, right? Or perhaps the story wouldn't have been quite as compelling if they published the specific numbers they used to calculate "TCO".
Also, are we to believe that the replacement apps are fully as good as the commercial alternative? MS Excel is not superior in any way to the open source alternative? There most certainly is a cost associated with productivity, far beyond desktop maintenance costs in many cases.
Considering that the police are using this software and their requirements are email and office apps then they don't need a lot of functionality. Hell you can use Google Docs and it would suffice.
Why would that be a requirement? Take any two things that aren't identical and each of them will be better than the other at something. You're assuming the comparison on net would favor Microsoft. For example, here's a short list of commands: grep, awk, sed, ssh, scp, rsync, wget, nc, dig, du, sort. These programs are not superior in any way to the Microsoft alternative?
Regardless, I'm not even suggesting who necessarily wins, I am saying it is a very important consideration that should be considered if you are truly trying to calculate an accurate TCO comparison.