The setuid binary was created (indirectly) by the Apache CustomLog directive, which is able to spawn programs to use as log targets. So it matters which user Apache runs as, because that controls which user creates the setuid binary and thereby which privileges you can gain.
Rereading the comment it also seems more like Apache is starting something that can become root somehow, I really don't think it is implied Apache is running as root.
Apache usually starts up as root so it can do setup that requires root, and then drops privileges to a user/group specified in Apache configuration. Most commonly the required setup is just binding to privileged ports, but one of the supported setup steps is opening log pipes. See the security note here:
