Nothing. It applies equally well. There is potential energy in free hydrogen molecules that stemmed from the initial low entropy conditions of the big bang that can be freed, for example, in the high-pressure environments in the cores of stars, or human fusion reactors. The act of fusing hydrogen molecules still increases entropy (i.e. we're going from low-entropy to high-entropy). You can keep fusing resulting elements and releasing energy, until you hit iron, at which point, you've reached the most stable atomic nucleus and you won't get any more energy out from fusion (or fission for that matter).
