[dpatru]

It is cheaper to make copies of software than almost anything else. This means that building network or a large customer base is very cheap, almost free. What prevents you from building a large customer base is not costs, but lack of demand and artificial barriers like charging a price. If you can make money by selling access to a large customer base, then it makes sense to go that route and remove every barrier to mass adoption.

Google does not have to work hard to sell its products. People are happy to use its search functions for free. And advertisers are happy to pay to access searchers. If Google charged for search, then it would have to work hard to sell paid search in the face of free alternatives. It would lose users and thus have less to sell to its advertisers. It's just easier from a marketing and business perspective to keep search free, or even pay people to search, and then charge for access to searchers.