Noone seems to talk about the cost of developers time working with Oracle. Most developers who know any other db hate Oracle, those that don’t assume that all DB code and/or ORM tools are difficult to use.
If I started a business that I believed was going to scale to Amazon proportions I might consider NoSQL solutions, otherwise I’d choose PostgreSQL, SQL Server (or indeed even Sybase now) over Oracle every time. I say this having worked (as a dev) with Oracle for 2 years – its terrible to work with!