True, but that mainly helps when it's the body of code that provides the key value, like in a large engineering project of the Linux-kernel variety. If it's the idea and algorithms that are valuable, and the code is a fairly straightforward implementation, then someone can just reimplement it and there's no GPL violation (subject to some gray areas). The only thing that could really keep that from happening is: 1) keep your methods secret; or 2) some variety of software patent.
