Pretty simple really. 1 out of 10 go-arounds leads to an unsafe situation, often due to non-existent manual flying skills.
So if you are an adherent to the "autopilot always on" school of thought and have trouble manually flying a go-around, airmanship would indeed dictate that you leave the autopilot on until cleared to land to reduce the risk of a botched go-around.
While I haven't seen a memo or SOP on this at my company yet, many instructors are already preaching this for landings at LGW because of the high number of GAs there. I think it's only a matter of time before this becomes part of many airline's SOPs.