As a case in point, EDB have spent quite a few man-years on their Oracle compatibility layer; and it's still not a terribly exact match, according to my colleagues who have looked at it. So that is a tarbaby I don't personally care to touch ... even ignoring the fact that cutting off EDB's air supply wouldn't be a good thing for the community to do.
What any commercial entity and the Community do are mutually exclusive and we can not and should not determine what features we will support based on any commercial endeavor.
From where I sit the "mutually exclusive" argument doesn't seem to be true - and in fact is something I think would be bad if it were. We shouldn't be afraid to add features to core that vendors are offering but at the same time the fact that the Oracle compatibility aspects are commercial instead of in-core is a plus to help ensure that there are people making a decent living off PostgreSQL and thus are invested in its future - and directly enticed to improve our product in order to get them more converts. I don't believe the community wants to compete on that basis nor does necessarily standardizing the layer and letting the vendors compete on consulting and implementation services seem a strong investment for the community to make.
There is no way to consider development plans without considering what the entire eco-system is doing: commercial and community both. A blanket statement like above is a good way to make sure you don't get too carried away with letting commercial vendors provide things that should be in core; but at the same time the hurdle becomes higher if those features can be had commercially.