Its a gimick that Pilkington use to up the price of their glass.
If you read the small print it states they still need to be hosed down and brushed with a soft brush now and then.
The glass itself is hydrophylic, which means the water sheers down the pane rather than bead so to flush the glass, they also put a chemical on the glass to help break down organic material, but its all rubbish, it can't break down traffic film or bird muck.
Matt