In general, note that the people demanding responsible disclosure (i.e. major vendors) also greatly benefit from it. (In general, creating and enforcing an ethical norm is not itself an ethically neutral act.)
Not sure I really agree. I think it would be courteous to politely inform yahoo! of their mistake. Potentially more rewarding, as well.
Lots of things that don't exist have Wikipedia pages.
In general, note that the people demanding responsible disclosure (i.e. major vendors) also greatly benefit from it. (In general, creating and enforcing an ethical norm is not itself an ethically neutral act.)