Gordon Van Gelder wrote a post describing F&SF's foray into free science fiction. He describes their policies then offers a survey to determine views towards online free science fiction. Most of the comments are from customers, not authors. So I'll offer my 2 cents. The reason I publish my time travel stories online is that I will end up making a lot more money here than I would ever see from print. Simple advertising such as Adsense, Amazon Associates, and Clickbank offer me more revenue than I will ever make from published work of science fiction short stories. Note that I am not referring to a novel. When my novel is complete I plan to aggressively market it to brick and mortar publishers because there is more money there (and possible movie rights !)
If I submit a short story to F&SF I might make $1000. That's it, that's the sum total of all money I'll ever make on that story. If however that story is available on my blog then advertising revenue can stream in for decades. The amount of money attributed to each story may be difficult to count, but that doesn't mean it's zero. Far from it.
Let's assume an author writes 10 stories per year. After 10 years that's 100 stories. It's highly unlikely that all or even most of those stories would be published. So let's assume that 10 of them would generate $1000 each. That's $10,000. The rest will never see ink on paper.
A well run blog with a reasonable amount of advertising could easily generate 2-5 times that amount. It's reasonable that over a period of 30 years those 100 stories might generate as much as $300,000.
Internet marketing has permanently changed the short story publishing industry. The change is irrevocable, dramatic, and liberating. More people will read my stories here than would ever read them on paper, as many as 1000 times more people. That audience has a monetary value to an author which cannot be matched by ink on paper. As a science fiction author I doubt I will ever submit a short story for publication. It's simple economics.