Earlier quoted context omitted.
This. Who is going to sign a Service Level Agreement for your postgres install? Support contracts are super important for enterprise.
EnterpriseDB? http://www.enterprisedb.com/ba/license-support-services-v3-0
If you're an enterprise customer with IBM, Oracle, or Microsoft, you know that you can have someone onsite within 24 hours if you have a critical failure, sometimes even sooner. You know that you can have people engaged 24/7 for as long as it takes to get you back up and running and you'll have not just technical people, but also incident managers who will keep you updated and help the engineers locate additional resources. They'll have someone sit in a conference bridge around the clock if you want, ready to provide updates.
Enterprises are also thinking about long time spans. With IBM, Microsoft, Oracle, Redhat, and others, they generally guarantee at least 10 years of support for their products, plus the ability for custom agreements that go beyond their normal support dates. Offering 3+2 is a good start, but that's not long enough. Remember, many (probably most) banks still have applications written in COBOL running.
Don't get me wrong, I think everyone should look at all the available options - free and paid. At the end of the day, though, there are a lot of projects where the risks and expected application lifecycle pretty much mandate the level of support you only get from the big companies.