One of the reasons for a focus on decisions and decision services is to complete the decomposition of the old, monolithic application (thanks Mark). Think about it. If you embed decisions - business logic - in your applications, you hide these decisions from view and risk those decisions becoming a liability when the world changes and they do not. Most application development techniques hide decisions inside applications. This makes development, and even more maintenance, very expensive.You might also delegate details to programmers when you want to have those programmers collaborate with business users on the required logic. Applying EDM you can empower business users to manage those decisions, which reduces the time to make changes and reduces maintenance expenses.
A colleague of mine (thanks Mark) pointed out that such as approach is the last step in the decomposition of traditional applications. Not so long ago, applications (especially enterprise applications) were monolithic, containing data, user interfaces, business logic, and process flow in one block of code. We then begun to decompose these applications - managing data in a database that ran across applications, using portals and other clients to manage the user interface across applications and, most recently, BPMSs to externalize workflow and build cross-application flows effectively. One more step is required - separating out the decisions and managing them so they too can be shared across applications. This could be the most important advance to date.