With its new Drop Tech Series Case for the third-generation iPad ($60), Gumdrop Cases has simplified last summer's Drop Series Case for iPad 2, seemingly without major compromises. Rather than using a full plastic endoskeleton, Drop Tech attaches hard plastic solely to the front of the tablet, curling over but leaving exposed the Sleep/Wake Button, rear camera, and volume rocker. A removable plastic screen protector is also included; we found…