Well, I worked in an enterprise that used Python for a lot of thing, and one of my friend wrote Ruby in a gool-ol Insurance companies, so I don't know how much you can really say that they are not enterprise ready, but it's true that Java/C# are more used for the "big stuff".
What it mostly come down to is support. When you choose Microsoft and Oracle, you can call them at midnight on Christmas Eve and yell at them because its doesn't work, and they will fix your problem. For those mission critical applications, its very, very important to be able to do that.
They also sell more integrated solutions that are pretty much guaranteed to work together. If you take C# with SQL Server and Windows Server, they integrate pretty tightly. Same thing with Java/Oracle or IBM on Power with DB2. Those solution have complete tool to manage them that fit with what is existing (user are managed trough Active Directory, it can work accross continents, completely localised in swhahili, etc). If the organization grow and need to integrate a new component, its usually pretty easy to do so with those big enterprise solutions.
In the end, its not really the language itself, it's wether their is a big company behing that can sell tool, solution and support.