As I said twice now, they can't release the Harrier on Steam without somehow linking your digitalcombatsimulator.com account with your Steam account, since you need your dcs.com account to run the module.

This link has happened with some games already, not just for copy protection, for example if you want to go on the official Assetto Corsa forums (not the Steam ones) you have to log in with your steam account and link it. Paradox forums do something similar as well.