The 1570 has more features and options for outdoor use as a mesh AP: fiber SFP and cable modem interfaces, higher Tx power allowed. I think environmentals may be better but not sure. The IW3700 has smaller enclosure (thinner with mounting holes to place on a flat surface) which is important in the industrial setting where space is a premium. I can see 1570 on a pole as a traditional mesh AP, and IW3700 in a bridge mode on the side of a truck or some other moving equipment.
Cisco folks should weigh in here...
