Short answer - "NO" they are using it as a "Marketing Term" to communicate that they are opening up an API for custom extension. I would expect the user experience to be like the original iphone experience - Very Very Limited or turn into something like "MySpace" very quickly - full of security exploits and risk.
What would be a killer apps? Depends on the implementation of their security and sharing models. It does have the potential to create rich communities of common interest around specific topics if someone does it right. But I was unable to login to the link that you shared - so it does not make me optimistic at first glance.
A "Developer Platform" is defined as:
The computer on which the software is being written. Sometimes, the term is even narrowly down to the tool(s) running on that computer. For example, your PC or notebook as a development platform (running Windows or MAC, UNIX, etc). Or Eclipse as the development platform to write Java or any other programs.