For some insight into the point of view of a web developer being "hit up" for partnerships etc, you should give this article a read. The author is a comic strip artist and writer, but there are enough parallels between the two industries to relates his story to software development as well.
(part 2 is the good stuff)
If after reading this your paradigm hasn't been sufficiently shifted, here's the bottom line:
1. It is not reasonable to expect a web developer to assume most or all the risk of a start-up.
2. Web developers with free time are probably working on their own great ideas, or working as a freelancer for money.
3. An actual well-planned good idea can be funded by angel investors, who will then pay for the web developer to make the idea become reality.
4. Most unfinanced entrepeneurs who post requests for free coding haven't worked their idea through the pragmatic grinder-- the idea is completely undeveloped, undocumented, untested, and unproven. There is usually zero research done to see if there is any market for the idea, and usually less than zero effort put into planning the marketing of the idea. They just think the idea is so awesome that if they can only get a web developer to spend 3,000 hours to build it, people will magically buy into the product and everyone will get rich beyond their wildest dreams.
5. And finally, money talks, BS walks