If I maintain a free, US-based, ad-supported website which caters to Iranians (and so pay no Iranian taxes), do I forfeit the right to an opinion on filtering by the Iranian government?
Google has datacenters in the UK, so I think that's one fault in your argument. Also, Google sells ads, search services, email, office tools, and other things. Yours and my personal use of the service may cost us nothing, but I'm sure that Google sells millions of dollars worth of services to customers in the UK.