The Java DB, or better yet, the JRE DB, is just a RFP item.
Sales and marketing:
Companies routinely add functionality to a product that will never be used by a client. The reason for the un-used features is to meet an entry on a Request For Proposal (RFP). The sales department can then present the functionality to potential clients.
Many times a RFP item is something that multiple clients have requested, but serves little or no purpose. [The absurdity of the RFP are well understood by people that have worked for the Federal government or Fortune 100 companies. After 4 years on the NASA's Space Station Freedom project, I can tell horror stories about the RFP process.]
Choice and discontentment:
Embedded Java databases have existed for years. As Java developers, we have the added luxury of picking the database of our choosing. [Yet, some have argued that all the choices have bred discontentment toward Java.] Microsoft's claim to fame is their one homogenous, well-integrated, do it all environment. Even though Microsoft VisualStudio falls way short of free tools like Eclipse and NetBeans, and the .NET architecture is lacking features like an Object/Relational Mapper (ORM), the developers don't have all those decisions to make, they just make what they have work.
Microsoft has introduced the embedded database with the release of SQL Server 2005. As it matures, the database will become a standard component of the .NET platform. Microsoft already provides SQL Server Express for free, which can be embedded into application clients.
So, what does Sun do? Introduce an embedded database. Sun has to have that RFP item checked off the list.
As Microsoft has taught us, it is not necessarily about technology feasibility, competences, or merit, but marketing. Microsoft has satisfied many RFP items in name, but not in spirit.
Welcome to the world of reality. When Jon Stewart has a book author on his show, Jon Stewart did not necessarily think the book was a good idea, rather the publisher bought airtime.
I personally think Sun could spend the energy more judicially by cleaning up the Java API of the deprecated code. However, I am not a marketing guy.