“Ignoring Twitter is like letting the phone ring. Twitter is not a parallel universe for egocentric celebs and chatty customer services. It is a dynamic forum in which a CEO can lead from the front, extend influence, impress stakeholders, set a corporate benchmark and show staff how to engage with their stakeholders," said Robert Glaesener, chief executive of Talkwalker.

Unfortunately Twitter IS a place for egocentric celebs and chatty customer services.  CEOs come and go, but FTSE 100 companies stay around.  I can see a strategy for keeping them separate.  Also, there are other, more company private ways to influence and impress shareholders rather than using a public forum where even the most vile company haters are given a say to twist everthing put out by the CEO including price sensitive information.  My first company traded on the LSE.  They have extremely brutal rules about the timing and disclosure of information to any subset of users that even the most sophisticated CEO could easily get in trouble with.  It's just not worth the pain for the tiny, little benefit.

You're right, the potential liability seems to outweigh the potential benefit for most.