Didn't that US site concerning the outside runs state that it would become law in America to keep cats indoors all the time? I think the bird lobby would like this, especially pigeon fanciers.
(Years ago I dated a vet and spent a weekend with him while he was on call. He was called out to a cat who'd had its claws ripped out by a neighbouring pigeon owner!) This is true, and horrid.
A while ago I saw that ex-Goodie guy (can't remember his name) speaking about how cat owners should be forced to keep their cats indoors in order to save the bird population. Personally I think song-birds would be better helped if pesticides weren't used.
Maybe that's where your mum heard of this?
I prefer to give cats a flap and a litter tray in the verandah. But Polly's ears mean I have to keep her in during the day, so I give her freedom at night. She just stays in and sleeps anyway!