I don't know much about IBM products but I'm a heavy Oracle DB user in the process of migrating to Postgres due to simple problems, cost not being one of them. In fact, you will see a lot of users still using very old Oracle versions and getting full support from oracle.
Oracle (DB product) is the wrong choice for most startups, I actually wrote a post about that some time ago: http://eduardo.intermeta.com.br/posts/2013/2/1/this-is-why-y...