Actually MS gives services and software free all the time. For example their low tier development tools are free. They got in trouble with the justice department for giving IE for free while there competitors was charging for browsers...
They give it away to lock people in further down the line like all software companies. As someone in IT procurement believe me that MS is very rarely value for money aside from the legacy effect
And I think you need to read the IE story again. They got in trouble for forcing use of it with their OS because other free options are available and its anti competitive.
No one sells standard browsers.