My personal opinion is that Oracle is very dedicated to the entire Eclipse ecosystem as well as to JDeveloper. It's about choice. There is an entire free download product that is continually being enhanced called the Oracle Enterprise Pack for Eclipse (Oh-Pee is how we say it within Oracle). In fact I believe it was one of the first, if not the first commercial IDE to support the latest Eclipse 3.5 Galileo. http://www.oracle.com/technology/products/enterprise-pack-for-eclipse/index.html OEPE is targeted for Java and JEE developers and is mostly about supporting the Java standards. Additionally, the majority of the TopLink code was donated as the EclipseLink project and is currently the JPA reference implementation. Just take a look at the presence has at the next Eclipse conference and I think you will see that Oracle is committed to Eclipse. http://www.eclipse.org/eclipselink/
When you get into the "upper-stack" components like SOA Suite for integration and WebCenter Suite for enterprise portal development, and Oracle's Application Development Framework (ADF) that Oracle strongly recommends JDeveloper. Those products have been based on JDeveloper for a long time and the user-experience developing for those products is extremely smooth because Oracle can influence everything about the IDE. If you want to do Java and JEE development in JDeveloper, you can do that too. It's your choice.
"I have not the slightest confidence in 'spiritual manifestations.'" -- Robert G. Ingersoll