The Scottish government recently ran a TV ad in which they advised everyone to unplug unattended rechargable devices. Presumably they wouldn't have paid to run such an ad if they didn't think there was some kind of risk involved, however small.
HSE also advise not to leave electrical equipment, such as a TV, on 'standby' if it is unattended. This was because they were aware of 5 (repeat, 5) cases in the UK where a TV on standby had caused a fire. So however small rhe risk, there's still a risk, I guess.