They have a minimal, but very functional set of features that are more than adequate for many people, but may leave power users dissatisfied, at least initially. Lately, I find that feature less important. The Pilot's universal Find button, and the device's speed are an adequate substitution for data linking. Also, the built-in applications are small, letting Palm keep the ROM small. The small memory requirements of both the Pilot OS and the built-in applications means that Pilots cost less than comparable devices.
Memory is the most expensive component of a handheld computer.
Sony's PIC-2000 Magic Cap device has similar memory requirements. A Pilot sells for less than half the price of a Newton. Consequently, more people buy them. I don't mean to imply that people aren't buying Newtons or PIC-2000s. Event driven, not object oriented The Pilot's speed is determined to a certain extent by the choice of processor, the speed at which that processor runs, and other hardware factors.