Why haven't the new network TV shows gone to HD?

While it may cost you only $2000 for an HD camcorder, a professional grade HD camera costs over $20,000, and if you use HD-SDI, versus SD-SDI (which they probably use now), you have to upgrade all of your switching routers, your capture equipment, your editing suite, better lighting (since HD will show those things better). It's not just a matter of "buying a new camera".