Smartphones are expensive and can sold for high sums. It's easy to sell a stolen smartphone, because the hot phone can be activated on another network, but not after Halloween for GSM smartphones.
The FCC and CTIA are working with police departments to thwart the black market by a stolen smartphone database, education, remote data wipe and prevention.
Taking smartphones are like taking candy from a baby, the devices are small, worth up to $600 each and can be nabbed from a pocket/purse or coffee house table, easily. They do have unique EMI numbers that will be traced in the future.