Well... Superman is not 'about' those things, anymore than he's about a red cape and blue tights, but they have become symbols for what Superman is about. And while the powers aren't necessarily baked into his themes - aside from the comfort of familiarity that his powers bring to countless millions - the idea of being superhuman, in its most basic form, involves being superhumanly able to do things everyone does. Super speed, super strength, super senses. Flight is a metaphor for freedom, which a superhero, theoretically, has more of. Heat vision and Superbreath may seem pretty random, but even the hot and cold nature of his tertiary abilities has a very primary color, literally elemental effect. His powers don't make logical sense, but they make thematic and emotional sense.