This is mainly because appliance manufacturers have no reason to design their products with efficiency in mind -- after all, they don't pay your electricity bill!
The IEA states that devices on standby account for 1% of global carbon emissions. This isn't very much, but it is growing. It is also unnecessary and avoidable. They go to state that:
New technologies have emerged making it possible to reduce standby power by as much as 90%while maintaining all features that customers want. The most important innovations are higher efficiency power supplies and improved circuitry designs.
I haven't been able to get a definitive answer about whether it is currently better for consumers to switch off devices in standby thus saving electricity, or whether it is better to leave them in standby thus extending the life of the appliance (personally I am switching off as many devices as possible). However I have become convinced that consumers should put pressure on manufacturers to use more efficient standby designs, or not use them at all. In 2005 WWF Switzerland launched a petition to stop the energy waste caused by standby functions of electric appliances. The petition aims at putting pressure on producers and retailers to make products more energy efficient. There is not an equivalent petition for the UK, but the WWF do have a campaign to stop climate change. Why not take 90 seconds and sign the petition now?
(Today's picture is of the family at the Ladybower reservoir yesterday)