You can support locks for HTTP if you need them (WebDAV does), though I would argue they aren't necessary for a large number of useful tasks. You don't have to

You can support locks for HTTP if you need them (WebDAV does), though I would argue they aren't necessary for a large number of useful tasks. You don't have to implement all the semantics of a filesystem in order to benefit. The main benefit comes from making a filesystem-like construct accessible in the browser. As I said before, Google Drive is a good example of this (and it's an object system, so that's an orthogonal issue), but it's a complicated protocol (as is S3) in a walled garden.