There are at least three major differences between using Google's services vs. Microsoft applications, besides the economic cost, which as you correctly point out is not really relevant to real freedom.
1. You can access Google's significant services using entirely Free software and open protocols. That is very different than running an entire proprietary operating system on your own computer, regardless of if its in a VM or not.
2. Unlike Microsoft's major products, there is no attempt at lock-in with Google's products. You can fairly easily download all your email, calendar appointments, and contacts from Google's on line applications, and upload them to a new provider of choice any time you want.
3. Google is very friendly to the Free Software / Open Source community, unlike Microsoft which is essentially at war with it. Google both heavily uses Free software, and also contributes back to the community. This is fundamental, with deep implications for the future of the two companies, and should matter to you, if you are deciding between using products from either Microsoft and Google - even if the Google product is proprietary.
Do you _really_ not see any difference other than the price tag?