...and, let's face it, the relative complexity of a skyscraper compared to a computer software program, given equal cost, is very, very low. A skyscraper costs hundreds of millions to construct. An equally costly software project would be something like the entire lifespan of the .NET Framework including the CLR, Standard Library, C#, VB.NET, Silverlight, all of the "Enterprise" features, etc.
Also, software isn't really construction. It's built by the people who design it, for the most part. Imagine a skyscraper (or car, bridge, etc) built entirely by engineers. Yikes.
We can't afford a single skyscraper collapse, but we can usually afford to use bad software.
In fact techniques exist to produce software with near-zero defect rates (primarily relying on extremely thorough code inspection, IIRC), but they're far too expensive for commercial use.
Also, software isn't really construction. It's built by the people who design it, for the most part. Imagine a skyscraper (or car, bridge, etc) built entirely by engineers. Yikes.