actually valve owns steam and valve isnt owned by vivendi. Vivendi is the publisher of HL2 though (atleast the box version, not the version you can buy through steam).
And just because two companies share the same owner, doesnt mean that they will help eachother out. It depends on what is allowed by the country (to prevent abuse of monopoly position/getting a monopoly) and how the owner wants the two companies to interact.
And just because two companies share the same owner, doesnt mean that they will help eachother out. It depends on what is allowed by the country (to prevent abuse of monopoly position/getting a monopoly) and how the owner wants the two companies to interact.