Is volunteering free service such a good thing?

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I write from India and I have a guess about American (or predominently Christianity influenced?) culture - that volunteering to do free service is considered a very commendable and essential quality in life. Volunteering to do a free service as a member of a religious group or spiritual organization or as a charity (with or without religious back ground) for the upliftment of the downtrodden or for the benefit of the society is one thing. But how about volunteering to do some free service even in commercial establishments? Take for example: Wikipedia. I understand most of (or all of) the reference stuff out there are being contributed voluntarily. I think Linus has been developed by the free contribution of numerous software professionals. There are many such examples out there. I understand may websites thrive by utilizing the free service of some knowledgeable people and they "reward" the members by giving some "stars" and "T-shirts" once a while and nothing else. Why do people do it for free? For ego satisfaction? For a sense of self-importance? Or is it part of a culture? Take for example, Helium website. It is a commercial website, which accepts and publishes articles from numerous writers across the globe, get advertisement revenue and share a portion of it with writers. But they have "site stewards" - to monitor the various major title groups and help writers, co-ordinate with them, monitor contents etc and they all work for free! People seem to volunteer to do that work in all eagerness expecting nothing in return! It is simply baffling to me. Why should people offer free service to a commercial organization? If it is a service organization or a religious organization it is totally different. Just because people offer services for free (for ego satisfaction, pride or whatever), are not the commercial organizations exploiting people? If such sites were to employ people for doing such work, they have to pay salary. But by simply utilizing people's tendency to offer free service, is it correct on the part of an organization to happily make money (or save money) by the strength of free labor? I doubt very much whether such a way can ever work in India. Here, people do volunteer service, but it is mostly religion, spirituality or charity oriented. Some amount of free service can be seen in political organizations too in India, where grass-root level members offer so called free service, but they too tend to do it for food, some perks, or by eying for some future benefits from the powers-that-be. What do you think about this? Is it a cultural phenomenon? Is it a trend encouraged by religion? How far is it okay for commercial organizations to exploit free service for self-serving ends? Do you have any personal experience on this matter?