It does if you then share the resulting software. And I think if you make an improvement just for your own enjoyment, you'd be a better person if you shared it back than if you didn't.
Anyway, the GPL is there to protect final users and not the maintainer of the project. And if a software is running on someone else server, you are not the user of that software. (Although you use the service and give the data, but that's another problem)
