I wouldn't say "I write for myself," nor "I write for my readers." I write because I enjoy writing. I place it online and share it with others to receive feedback. I place it on B&N, Amazon, etc so that I might make some small amount of money from it, and others may enjoy my work.
Money and readership are hardly my goals in writing. They are nice, certainly. It's always enjoyable to be paid for something you love, and sharing your work with others is always enjoyable.
But, my primary motivation in writing is enjoyment. My primary motivation in showing it to others is constructive feedback, so that I may improve. I perform because I like it and want to improve at it. Money is just icing on the cake.
Have I ever considered a "target audience?" No. Do I know when something is not appropriate for a certain age range? Yes. Do I edit my work a little when publishing to a site that doesn't allow cuss words? Yes. When works are not appropriate at all, I simply do not post them. But that is the extent of "thinking for the audience" that I do.