Mains sockets and star earth - can anyone explain?

The vendor of my mains isolation strip advised me the following by email:

To avoid any unwanted grounding problems and to get the best performance out of your system you should power all electronics of your system, no matter if they are wired with or without a grounded cable  out of one wall socket (starred earth reference)

Can anyone explain what this means, especially with reference to starred earth?

I now have my amp plugged directly into one socket of my 2-socket wall plate, and my isolation strip (for my sources) plugged into the other socket.  What difference does this make to earthing?  Surely, a neighbouring wall plate will have its earth connected to every other wall plate in the room by parallel wiring between the plates.

Note: all my cabling is shielded with the shield connected to the earth pin.