AWS Data pipeline is mainly used for data driven workflows that are popular in Big Data systems.
AWS Data pipeline can easily copy data between different data stores and it can execute data transformations. To create such data flows, little programming knowledge is required.
Amazon Simple Workflow Service (SWS) is mainly used for process automation. It can easily coordinate work across distributed application components.
We can do media processing, backend flows, analytics pipelines etc. with SWS. So it is not limited to just Data driven flows.