Valve has had a tiered system for a while now, it does still start at 30%, but then it drops to 25% for titles with >$10M in revenue, and again to 20% for title

Valve has had a tiered system for a while now, it does still start at 30%, but then it drops to 25% for titles with >$10M in revenue, and again to 20% for titles with >$50M in revenue. They switched to that model after the major publishers started leaving Steam and releasing on their own launchers instead, so Valve structured it to give those AAA juggernauts a discount while still taking 30% from the small fry who basically have no choice but to release on Steam.