Among small or early stage startups? No. Oracle charges kingly rates to go along with their kingly title, rates which pretty much only big companies can pay. Oracle DB setups often tie into other Oracle products as well, which can be more useful to established and larger companies.

Your professor is correct in that it's widely used amongst such companies, though other competitors are very often in place as well such as Sybase or Microsoft SQL Server.

The right tool for the right job (or in the startup world, the tool you can afford.)