(Replying to myself, yes, but for further clarification:)
In such organizations the "whatever software you want, provided it can do the job" policy is usually official but unsupported. At least where I work, developers can run whatever OS, office suite, editor, etc. they want, provided that it doesn't hinder their ability to get their work done. So yes, we can "use whatever we want", but that freedom ends if we start relying on our IT support staff to support non-standard stuff.
Also understood is that a great way to end the policy would be to demand that everyone else switch formats so as to allow you to use your chosen piece of software.