The reason that moving data from a transactional platform to a warehouse platform is not trivial is because you actually have to have ETL processes in place to transform data from one architecture to another.
A data warehouse has nothing to do with the mechanism that stores it. It is a design that comes with its own challenges just like transactional systems do. Transactional systems are optimized for writing. Warehouses are optimized for reading. They way you choose to execute those optimizations is up to you. But getting data from one of those systems to the other is never going to be trivial, and there is no general purpose tool to get things from one format to another because the warehouse structure is too entity-specific to generalize beyond a certain point (and that point of generalization is really the process of creating the design. See the Kimball group's books for more information.)
Redshift is not a data warehouse anymore than Postgres is a data warehouse. In fact, Redshift is a fork of Postgres that leaves out the functionality, data types, and indexes that make it difficult to scale horizontally. Postgres also isn't a data warehouse. Nor is it transactional system. It's just a tool that you can use to build either one of those things with.
A data warehouse has nothing to do with the mechanism that stores it. It is a design that comes with its own challenges just like transactional systems do. Transactional systems are optimized for writing. Warehouses are optimized for reading. They way you choose to execute those optimizations is up to you. But getting data from one of those systems to the other is never going to be trivial, and there is no general purpose tool to get things from one format to another because the warehouse structure is too entity-specific to generalize beyond a certain point (and that point of generalization is really the process of creating the design. See the Kimball group's books for more information.)
Redshift is not a data warehouse anymore than Postgres is a data warehouse. In fact, Redshift is a fork of Postgres that leaves out the functionality, data types, and indexes that make it difficult to scale horizontally. Postgres also isn't a data warehouse. Nor is it transactional system. It's just a tool that you can use to build either one of those things with.