Programmers write code, QA specialists (really just a specialized kind of programmer) make sure that it works, designers create flows, layouts, copy and graphics, and sales people sell. Sure, someone needs to keep an eye on costs and revenues, and manage the business – but that’s not what most product managers do.
So do we really need product managers? Or do we just need someone to make sure that someone is leading the team and taking accountability for delivering something that consumers want and customers pay for? This seems to be the approach that Facebook takes.