But that's because Valve can start imposing fees (per year or per month) to keep accounts open instead (with 65 million accounts, a $10/month fee could pull in an extra $6.2 billion annual income even if only 80% of users sign up).
Oh, come on. Do you honestly believe that's even a possibility, much less a probability? Exactly what would they be charging for? Access to our already purchased content? Access to the Steam Store? Neither of those are even remotely likely. The former would lead to lawsuits, and the latter would lead to people abandoning Steam in droves.
I'm honestly intrigued what you think they would be charging for.