There are very many people to whom it is not obvious that this only means electricity. Probably more than half the people that will see this headline, whether on HN or elsewhere. Think of all the environmental activists with no physics background who can't tell a Joule from a Watt or a Volt from an Amp. (There's nothing inherently wrong with not knowing but information should be presented so that it doesn't mislead, and people like that are probably part of the audience for the article.)