The most important factor is a technological advance: engine immobilizer systems, adopted by manufacturers in the late 1990s and early 2000s. These make it essentially impossible to start a car without the ignition key, which contains a microchip uniquely programmed by the dealer to match the car.
Criminals generally have not been able to circumvent the technology or make counterfeit keys. “It’s very difficult; not just your average perpetrator on the street is going to be able to steal those cars,” said Capt. Don Boller, who leads the New York Police Department’s auto crime division. Instead, criminals have stuck to stealing older cars.The article goes on to note that while thieves still target older cars, the value of these cars' parts is on the decline as time goes on, which reduces the profitability of car-theft rings and chop shops. This means that while older cars can still be stolen, the likelihood of them being targeted will decline as their parts lose value.
This particular explanation may not apply to all thefts -- the article notes that cars stolen in California are often taken for use in drug trafficking -- but it is good to see that a decline in thefts is occurring as the profitability of stealing cars declines.
This story is also worthy of attention in light of a push for smartphone manufacturers to include "kill-switch" technology in their phones. This technology would allow smartphone users to disable their phones remotely in the event that they are stolen, rendering the phone useless to the thief or the thief's customers. California is in the process of passing a bill that would require this technology in new smartphones -- the bill recently passed in the Senate and is now before the governor. For more on the California bills, I recommend this coverage by the Washington Post and CNET.
The Times presents convincing evidence that removing the profit from stealing certain cars deters the theft of those cars. Kill switches remove the profit from stealing phones by rendering them unusable once stolen, and would likely deter the theft of smartphones in a similar manner.
The Times' report on declining auto theft rates is encouraging news (especially to me, as an owner of a Honda Civic that is just new enough to be an unappealing target for thieves). I hope that makers of smartphones and legislatures considering bills similar to California's learn their lesson from vehicle technology so that this type of theft deterrence can be applied to more and more goods.
[UPDATE 8/17/2014: I have edited the title of this post]