Programming with sockets is a much lower level activity than CORBA development.
A socket basically consists of two endpoints, usually two computers connected across a network. Those that have done it will tell you that it has a steep learning curve, requires working at the data buffer level, and can be difficult to debug and optimize.

RPCs were a result of the software industry realizing how valuable sockets programming could be, while desiring the ability to build distributed applications at a higher level. RPCs solidified the concepts of client and server by allowing a client to request services and have them provided across a network. The key to the model is that Remote code in a Procedure at the server is run as a result of a Call by the client. RPCs allowed developers to make use of sockets at a higher, more intuitive level. CORBA borrows heavily from the RPC model, but strives to make the entire process as open as possible.

In addition to sockets and RPCs, many database vendors and third party tools vendors have created development tools that allow database access and other forms of distributed computing. The primary weakness in these tools is that they only interoperate with tools from the same vendor and tend to make it very hard to allow distributed applications to keep up with changing business processes. This problem does not exist in CORBA-based systems.