In a multisite install, certain settings are disabled by default (in this case the Update Services setting was switched to default to false in WordPress version 3.0). The multisite install sets the enable_update_services_configuration filter to return false, which hides the setting from being available in Settings > Writing.
In the page you linked to, there’s a link to the Activate Update Services plugin, which is a fairly simple plugin that switches that filter to return true.
Many hosts (and hosts managing a network of WordPress sites) place restrictions on sites “calling out” or pinging other services, so I suspect that might have been part of the reason for defaulting this to be switched off. If you’re managing your own network, you could look into the above plugin. If you’re working with a host, they might be able to tell you what their policy is regarding this feature.
I hope that helps!
