Actually, they WOULD work. But they wouldn't work RIGHT. Each arrangement is designed to have X amount of metal area with Y amount of clamping pressure distributed across it. When you change the bolt-type, you end up with a very small area of the bolt actually pressing against the seat. This results in 'Y x whatever' force on 'X / whatever' area.
This could be a very bad thing, under certain circumstances. Things could crack, or the bolt might work it's way loose.