This basic tenet holds true for all of the DG technologies based on burning fuels, which are the most likely near-term DG systems. Sorry, the analogy still fails. Here the similarity ends. To gain greater PC power, engineers make ever-smaller components of increasing density, thus expanding the total number of microscopic electronic devices per square inch. True the sun is limitless, but it's just too darn far away to produce high-density power, hence the need for lots of acreage to gather the dilute power.
Wind power suffers from the same problem.
The materials that make the electrochemical magic happen are expensive. Fuel cells run on fuel, ideally hydrogen. We will, to be sure, eventually see real advances in fuel cells, but they're no threat today to the gigawatts of conventional generation. Most of the current market hype surrounds microturbines, which are really just very small jet engines tied to an electric generator. They still cost too much, and despite the hype, you still can't buy one.