The key is efficiency. The more efficient a system is, the less redundancy it has to cope with problems. The satellite systems mentioned have quite high redundancy - I regularly get 12 GPS satellites visible on my unit, for example, and I really only need 4. Even this Iridium system has some redundancy.

From The Register: "This satellite loss may result in very limited service disruption in the form of brief, occasional outages," the firm said, adding that the company expects to have a network solution in place by Friday, and will move one of its in-orbit spares to permanently replace the destroyed satellite within 30 days.

Efficiency is the enemy of reliability.