It's hard to think of a situation where a new startup would use Oracle; it's a massive cost compared to alternatives and while it does offer some advantages over other DB choices those advantages are not very compelling for most uses.
For example, we did some rough testing recently and found that Oracle was faster for report generation than MSSQL but we can double the processing power assigned to the MSQQL to get equivalent performance for a fraction of the cost of Oracle licensing.
If you're a startup selling services to large enterprises you may be forced to use Oracle because it gives your customers more confidence in your solution (assuming you're offering a service where you storing information on important assets on behalf of the enterprise).
For example, we did some rough testing recently and found that Oracle was faster for report generation than MSSQL but we can double the processing power assigned to the MSQQL to get equivalent performance for a fraction of the cost of Oracle licensing.