I'm in agreement with basically everything Felix Salmon has to say about the economics of quality versus quantity in online journalism, but one extra wrinkle that he doesn't consider is worth attention. One of the main changes the Web has brought to the periodical business is that really well-done non-newsy features now have the ability to live forever. I first read Edward Jay Epstein's 1982 article on the diamond business years ago on the Atlantic's website and I still find myself regularly recommending it to people. I totally missed Will Saletan's series on memory for Slate when it was published in the spring of 2010, but I saw it last week and it's great. This 1968 profile of Martin Luther King Jr. my grandfather wrote for the New York Times Magazine shortly before he was assassinated is interesting to this day.
The existence of this deep back catalog is great for readers, but not necessarily as rewarding for the forward-looking production of longform pieces. Each day—each hour, even—all previous "newsy" items become obsolete and the demand for new newsy items is robust. But the existing stock of well-hewn blocks of substantial prose is already very large and it no longer depreciates the way it did in print.