I'm guessing that the people who decided that those characters bore any resemblance to a horse or a woman are the same people responsible for naming the constellations.
That's because you're seeing them after literally thousands of years of evolution and simplification.
马, for example, is the simplified form of 馬, which is traceable back through the millenia to a pretty recognizable picture of a horse back around 1300 BCE or so. (http://en.wiktionary.org/wiki/%E9%A6%AC#Etymology)
Quite the opposite. Once you have engraved in your brain the shape of these characters they become the very representative shapes of the things they draw. It is not a matter of resemblance, just as most caricatures do not resemble the model, but the model is still immediately recognized. Another analogy is the sign indicating lifts in airports: it do not resemble any kind of real life lifts, but everyone still understand it, without even having a sound for it. So are Chinese characters. If you don't believe me I'll pardon you: a long familiarity with them is required here.
