In producing the ocean heat widget, Skeptical Science acknowledges that bombs aren't really going off in the ocean; therefore, it's an analogy, not a scientific description. But the analogy is an measure using a unit that is both large enough to describe the quantity of energy at work and within the comprehension of most people who will hear the un-examined claim that global warming has stopped.
By the way, I drew the globe, and I do recognize the the Earth is not truly hollow and filling like a bowl. I hope the metaphor reminds people that the bomb analogy has the qualities of an analogy: not the real description but a useful metric among a population that does not have a ready appreciation for Joules, or other units of energy.
jg