If you're releasing your code, it's only to the customer. The one's who receive the code are only the ones who receive the binaries and ONLY upon request, think BMW's code they released upon a customers request. Sometimes it's better to use GPL or BSD, because some customers will not use your product if there is no code to guarantee if your company disappears they can't move on without you. Look at WordPress, their code's right there, and yet nobody can overshadow them yet.
Edit:
I agree with you, but I was mentioning GPL because you placed it in question. BSD is great, MS-PL is a little nicer if you need to protect any patents too.