Duh. Faults happen. They happen in non-cloud environment too. And it turns out that for most companies it's perfectly fine to have several hours of downtime once every couple of years.
Besides, cloud computing gives a range of possibilities not possible before. For example, our company sometimes runs 500 computing nodes on Amazon EC2 - that's more than 5000 CPU cores. Ten years ago it would have placed this cluster in the Top500. Now we can have it without paying about $1*10^6 upfront for less than 1 cent per CPU-hour.