Let's get past the pigeonholing here
I cover most of these companies extensively, e.g. on DBMS2. To summarize:
1. Postgres, especially in EnterpriseDB flavors, meets most needs for most organizations. That doesn't mean you should port your existing apps, although they do their best to make that easy in the case of Oracle or MySQL. But unless you're so small that it REALLY makes sense to consolidate vendors, or even to have a complete single-instance company-wide database, Postgres is apt to be a very good alternative for new projects.
2. The same is true, to varying degrees, of most other DBMS one could name.
3. The above article draws a false dichotomy. Going after the market that's willing to adopt products like MySQL is not contradictory to going after the markets that currently prefer Oracle.
4. Enterprise uptake has been slower for EnterpriseDB than Web/SaaS/ISV uptake. They even fired some enterprise salesmen late last year. But they do, at least under NDA, have a bunch of big-name enterprise customers.