Problem: Bloggers Work for Free?

Liberal journalism blog aggregator and opinion site The Huffington Post was sued in a class action in 2011 on the grounds that the blog had failed to pay the more than 9,000 bloggers who had provided content for the blog over a period of years. In submitting copy to The Huffington Post, bloggers knew they would not be paid, but presumably they valued the professional/political/personal exposure afforded by publication. The lawsuit, however, claimed the agreement to provide content without compensation had resulted in unjust enrichment for Huffington. AOL purchased The Huffington Post earlier in 2011 for $315 million; the bloggers sought approximately a third of the purchase price, asserting their contributions had made The Huffington Post that valuable an acquisition. In 2012, a federal judge dismissed the lawsuit, concluding that the bloggers had not expected money in return for their contributions to The Huffington Post.

Question

The law aside, does The Huffington Post have a moral duty to compensate the bloggers who knowingly gave away their content when that content subsequently proved to be instrumental in building Huffington into a valuable property? Explain. Do you feel a duty to pay others when you are the beneficiary of "unjust enrichment?" Explain.