The original bitcoin logo used to be a detailed, golden coin with a bunch of gradients. Looked a bit bad when you had to shrink it. The orange you see now wasn't by Satoshi but by a forum member named 'bitboy'.

I'd like to believe Bitboy designed it that way because Yellow/gold does not contrast well in white when the logo is shrunk down. Yellow works better for large buttons. The simple orange icon is good for small icons or for the web.

If I was personally designing bitcoin, I'd have made the logo purple, as green (the stereotype color of Fiat money / US Dollars) and purple are contrasted against eachother on a color wheel. I'd like to imagine Orange fits better for a 'electronic cash' however.