Since when was there an imperative to allow people to use their own devices? The whole idea is clearly being driven by the manufacturers of mobile devices as no network/security/sys admin in their right mind would allow personal devices on the network. My policy is exactly that and we check DHCP leases regularly and move all non-PC devices to the deny list. Mind you, for any of this to be useful you also need to have policies/proxies in place to prevent access to any medium that can be used to send data out of the network, so blocking Dropbox et al and webmail has to be implemented. When this is in place you have a solid argument for not allowing iPads etc to be used for work purposes as they would need to justify breaking policy just to use the device.