The answer isn't mysterious. Some documentation has moved online.
The rest has gone private: You buy it at Amazon, often from the same tech writers who used to write the "free" documentation that was built into the price of your product. (e.g. David Pogue used to be famous for writing excellent product manuals, and he is still famous for writing excellent product manuals, but now they're called "the Missing Manual series" and you must buy them a la carte.)
This used to be impractical because the Internet didn't exist. When you brought your copy of Microsoft Excel home from the store you needed a printed manual because, when you couldn't figure something out, your alternative was to (a) get in the car and drive to a store and buy a third-party manual and take it home, only to discover that it sucked and you needed to repeat step (a) again; (b) get on the telephone and speak to tech support people, perhaps slowly and haltingly, with no graphics or screencasts to help you; (c) pray that you had a local expert from your company's IT department; (d) give up, take the software back to the store, and buy some software with a better manual. It was the threat of option (d), and the extreme cost of servicing option (b), that drove companies to expend a lot of energy producing manuals.
Now we have lots of alternatives: Google, wikis, official forums, unofficial forums, blog entries from power users, Stack Overflow. And browsing and buying third-party manuals can be done from your desk, thanks to the power of sites like Safari Books and Amazon.
My impression is that the "unofficial" web-based options, combined with the third-party manual market, works fine for software that doesn't change frequently. (e.g. Photoshop -- my only problem as a Photoshop newb is that there are far too many manuals and tutorials available and I'm suffering the paradox of choice: I can't decide which to try first!) The big, new problem is that the Internet has sped up and de-synchronized software development to the extent that the docs can't keep up. I work with Drupal, a product that evolves so fast that the documenters can't work fast enough: they must produce and organize the docs for the older version, the latest version, and the up-and-coming version (which are all significantly different). And Rails is far less stable. I own a bunch of Rails books that are two years old, and they're increasingly obsolete. Given the lead time in producing books, you can't even get the damned things out the door before the products they describe disappear. (e.g. The Merb Way -- if Merb doesn't actually disappear after the Rails merger, it will certainly be a different platform, with a different audience, than the book authors were predicting six months ago.)
This used to be impractical because the Internet didn't exist. When you brought your copy of Microsoft Excel home from the store you needed a printed manual because, when you couldn't figure something out, your alternative was to (a) get in the car and drive to a store and buy a third-party manual and take it home, only to discover that it sucked and you needed to repeat step (a) again; (b) get on the telephone and speak to tech support people, perhaps slowly and haltingly, with no graphics or screencasts to help you; (c) pray that you had a local expert from your company's IT department; (d) give up, take the software back to the store, and buy some software with a better manual. It was the threat of option (d), and the extreme cost of servicing option (b), that drove companies to expend a lot of energy producing manuals.
Now we have lots of alternatives: Google, wikis, official forums, unofficial forums, blog entries from power users, Stack Overflow. And browsing and buying third-party manuals can be done from your desk, thanks to the power of sites like Safari Books and Amazon.
My impression is that the "unofficial" web-based options, combined with the third-party manual market, works fine for software that doesn't change frequently. (e.g. Photoshop -- my only problem as a Photoshop newb is that there are far too many manuals and tutorials available and I'm suffering the paradox of choice: I can't decide which to try first!) The big, new problem is that the Internet has sped up and de-synchronized software development to the extent that the docs can't keep up. I work with Drupal, a product that evolves so fast that the documenters can't work fast enough: they must produce and organize the docs for the older version, the latest version, and the up-and-coming version (which are all significantly different). And Rails is far less stable. I own a bunch of Rails books that are two years old, and they're increasingly obsolete. Given the lead time in producing books, you can't even get the damned things out the door before the products they describe disappear. (e.g. The Merb Way -- if Merb doesn't actually disappear after the Rails merger, it will certainly be a different platform, with a different audience, than the book authors were predicting six months ago.)