Steam don't ask me the activation too.
In fact in my registry there isn't the key for Bf 109, but there are for all other module buy on steam and on DCS web site.
DCS World 2.0 ask me activation.
I install first on stem, second on 1.5 and third on 2.0. Now in registry there is the key (after installation in 2.0)
In the folder installation of steam and 1.5 there isn't protect.exe