On the basis that you reap what you sow, I have paying clients from all over the world, Dubai, South Africa, Singapore, Brisbane to name but a few that I have met via this forum.
I may not be an Access Guru but my input here has kept my company in business for the past few years. Doing things for free are called "Lost leaders" or "Carrots". But everything is done legitimatly and above board. This is a market place or showing off you skills, if that is the road you want to go.
Some members do it because they like to keep their skills up to date and enjoy the community of this forum. Whilst others seek the expertese of the more knowledgeable, alas though there are limits to what peopl will do for free, and everyone has their own limits.
Why do I do it? well not only am I still learning new things from reading other posts I like to pass on snippets of information and code to help users resolve a particular issue. However this does not extend to writing complete modules, unless the exercise will benefit me at a later stage.