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As packet traffic threatens to rapidly dominate core lightwave networks, while IP-router architectures take aim at multi-Tb/s capacities, a fundamental architectural question is beginning to take shape. Will the simple expedient of directly connecting IP routers to wavelength-division-multiplexing (WDM) optical-transport systems offer decisive economies in emerging core-transport networks, or is there yet a role for an added layer of reconfigurable wavelength-level circuits interposed among router ports? By examining regular network topologies with uniform and random traffic, we show that by adding a reconfiguring optical layer one reaps large economies, so long as router ports remain marginally more costly than optical-layer crossconnect ports. These economies are essentially invariant with nodal degree over the range of interest in lightwave networks. They grow rapidly with network node count. The results offer a compelling case for incorporating optical-layer crossconnects in large datacentric core-transport networks, and suggest that the resulting economies will rise rapidly as the network itself grows.