So you buy software online via a service so why wouldn't you develop the same way? As the industry moves forward you'll start to see people expose solutions where developers can not only pull services into their application but also be able to develop those same applications online. I'm not talking about a closed platform with online development (ie a SalesForce Apex play) but a true Integrated Development Environment (IDE) available online with open languages and a directory of services developers can draw from. A true online 'plug-n-play' development environment. Pull the services, create your app, publish.
Think about it with a real world use study. A person in the shower comes up with a brilliant business application. They leave the shower then install an IDE, a delivery component (IIS, Tomcat, Apache), a database (MySQL, SqlServer), pull in some appropriate tool kits (some form of RAD tool), test/troubleshoot that the applications are functional and then begin to code. Instead, how about: A person in the shower comes up with a brilliant business application. They leave the shower, open their browser, create a username/login and beging coding. That IS the future.
There are some early companies out there that are trying to accomplish this. One that is getting the majority of the attention is Coghead. Coghead has an interesting approach as they are providing services but again a developer is trapped to only use the services that Coghead provides. The company that succeeds in this space will let the user community determine the services/applications that are the winner...not the company. I'm not saying that Coghead won't be successful (they will); just that they don't have a platform that will provide developers with the tools they need to build an application based on the services developers find the most useful.
Won't happen tomorrow; but in the near future you'll see companies that are providing this functionality. And they will be poised to truly become the 'hubs' of online application delivery.