Google seems to think that the modern Web, which is increasingly capable of delivering desktop-like application experiences, needs an application delivery channel, even though there is nothing to actually deliver—except URLs.
Ars Technica with a good piece on the new Chrome web store.
If a Web app is easily accessible and offers some functionality for free, it can more easily build an audience. The way people consume software on the Web is by clicking through a link and deciding if the destination has value. There is no overhead in doing that. A user can put a query into a search engine to find Web destinations meet a certain need and then open half a dozen in browser tabs and pick the one that looks the best.