Scratches and bites from Walker’s still kill, they always have, which is why they’re deathly afraid of being bitten or scratched by a Walker. The only change is that now they know that those scratches and bites aren’t what cause someone to rise again.
Scratches have never been proven to cause death from a zombie. The closest thing to that discussion is when Shane conjectured that scratches killed the two guards, to Rick, in at the City Municipal Works plant (when they were planning to drop off Randall).