PCI Compliance is more about the server that PowerStore will be run on. The database server and the web server need to be PCI compliant to ensure the safety of customers credit card information.
Processing credit card information off line *can be done* but you will need to make sure your system meets the industry requirements if you are going to do it.
those others that you refer to that are processing payments offline would have to go through the same processing of verifying that their system is up to the industry standards.