"Webservers like IIS uses a "worker pool," allowing as many open connections as its resources will allow."
But it can't have more 'resources' (aka threads) that a machine of the same spec. So we're talking again 1 to 1, or at max 2 to 1 to defeat them as well.
Apache simply allows you to configure the number of threads, so if the value is not low enough, there are no problems either. Experienced/savvy admins use stress testing tools before deployment.
Others get what they deserve.