The implied analogy with the US interstate highway system is a good one for many reasons. One is that only the Federal Government had the means and desire to set up such a comprehensive system, which has become so vital to the US economy. Corporations, while involved with the implementation, do not feel the same responsibility for supporting the basic infrastructure. Similarly, it is only the NZ Government that can provide a dedicated high speed link from NZ to the rest of the internet. The large capital outlay will preclude any privately owned NZ company from making such a long term investment in NZ's future.
Foreign corporations are unlikely to be interested.
The decision for the NZ Government to make such a large capital outlay will not be an easy one, but the long term benefits to NZ will be substantial. The immediate benefit will be to the people of NZ, particularly school children, who will then be able to investigate, and become part of, the new global information age. This cultural benefit, while substantial, pales in comparison to the long term benefits to the NZ economy. NZ's geographically isolated position will at last become unimportant, and NZ companies would be able to compete effectively for their share of a global marketplace. The technological and political details are admittedly quite complex, but the basic decision is a simple one.