Community
Oracle and SQL Server don't have a community. Please understand when I say that, I mean that the chance that you will get to talk to a developer of the core database is about the same as your chance of winning the lottery. By the time you do, it's probably because you found a bug so heinous that it couldn't be ignored and the only person who can understand your report is the guy who wrote the code in question. They have paid technical support and this support has proven in my experience to be generally competent, but not stellar. I have had to work around the problem that I originally requested help with about 40 percent of the time.
Compare this to MySQL and PostgreSQL, where just about anybody can speak to just about anybody else all day long. Many of the core developers of both the platforms can be found on IRC, met at conventions, contacted for contract development work, and for the most part, bribed remarkably easily with beer (hint, hint, wink, wink, nudge...
