Reading files from a directory or the web has always been relatively straight forward. ... Writing is the crux!
Users expect if an app can read content from a file / directory, it needs to work from the web too. Which is fine. But local access only works, because the browsers make it happen.
If you want to read files from the web, you need a file server software running on the server. The client has no direct access to the host file system, as in the local setting. ... So the mechanisms involved locally and the web only look the same but technically they are very different.
As soon as writing stuff back to the hard disk, or the web, the situation becomes much more complex, because of security concerns and restrictions.
-mario