Not buying that argument. Facebook just ran a Super Bowl ad, which cost over $10 million just for 60 seconds of airtime (plus who knows how much they paid for production and celebrities). That's part of user acquisition. And it certainly doesn't cost zero to attract advertisers (especially large corporate ones) who actually provide revenue.

In both cases, they are so ubiquitous that they aren't really after new users, just increased engagement/usage. And I'd bet Uber's per-user usage growth exceeds Facebook's right now.