[berberous]

Correct, these work in inclement weather, in various lighting conditions, at high speeds (60 mph down the highway), and include computers that OCR, extract the plate number, match against a large database, and notify on a dashboard laptop if a hit occurs. They also often include multiple cameras (e.g. to capture cars parked on the left and the right of a street.)

One of these companies does in fact have an iPhone app that police officers can use to query a national database, but it can't scan 1800 plates per minute as you cruise down a highway.

Here's an example large manufacturer of these: http://elsag.com/mobile.htm

Also note that they help local and state agencies obtain grant funding from federal sources, so I'm sure there's a bit of cost-cutting that could occur in a less bureaucratic and funded market. Also, these were like $30k 10 years ago, so prices are falling.