The big companies have got a Facebook/Twitter etc presence because their competitors have one. It's almost certainly a pain in the ass for them because as you mention customers will use it as a public platform to beat the company with when they're pissed off.

There was a period about 5 years ago when every company in the world thought they needed to have Facebook, Google+, Twitter, LinkedIn and so on. It was a serious case of FOMO (Fear Of Missing Out) as opposed to a genuine business case for social media.

I suspect we're going to see small and medium companies take a view that maintaining a presence on social media is still not generating ROI. As a result they'll consolidate to fewer social media platforms and perhaps at some point none at all.

If SMEs (or SMBs as they're known in the US) take this approach, big companies will slowly follow I'm sure.