Microsoft aren't 'selling' you the internet.

Because you can still use the internet with out paying any money to MS, how else can people download demos, watch films and get extra content? MMORPGs like Final Fantasy XI and Phantasy Start Universe don't require XBLG subscriptions to connect through the internet, but you just pay Square Enix and Sonic Team for use of their servers.
XBox Live Gold is a service provided by Microsoft, which Sony has decided to provide for free. For Sony, by making it free, offers one more reason to buy their consoles over the XBox 360, therefore they benefit from not charging. Microsoft I doubt would. From what I understand, it's a service that's maintained, like your internet subscription is as well as all of the servers they use for MMORPGs. WoW and FFXI like to charge money for usage of their online services, whereas Guild Wars and some smaller MMORPGs don't charge server fees. It doesn't mean they're selling free software.
If I understand correctly, XBox Live Gold is a service that costs Microsoft money to sustain. Nobody is charging money for the internet, but services provided through the internet.
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