The Object-Relational Problem

Every now and again I read someone's description of a software problem and I realize that I too have faced the same issue. Such was the case with Object Relational Mapping. Many of the software projects I've worked on have presented this challenge of how to map objects to database tables. And in each case my team came up with a solution that worked. What I didn't realize at the time was that the problem and solutions I used solve the problem were common enough to be given a name.

So now that I have confirmation that what I've been doing is actually correct (albeit not ideal), I'm curious to know where the true object-oriented databases are. I know there are a few packages and add-ons out there, but they're all from small players. Why hasn't Oracle, IBM, Microsoft, or Sybase stepped in to this arena? Surely there's a market large enough to support such a product especially since many companies have made the shift to object-oriented design and development.