Even as designers are trying to reduce cost, the need for dependability is increasing. A key reason that systems have to be dependable is that they have become an essential part of the fabric of our lives. Communications, transportation, medical care, and other applications are assumed to be continuously available for our business and our society to function.
More and more embedded applications are becoming directly or indirectly safety-critical. Whereas it used to be that electromechanical backup devices ensured safety, some of those functions are migrating to digital hardware -- and sometimes even software. Also, as embedded systems have more complex functionality, it is becoming very difficult to say what seemingly innocuous feature might trigger an accident as a secondary effect (for example, a bug that engages cruise control when the driver isn't paying attention might cause the driver to panic stop and create a pile-up, if it doesn't create a crash outright).
But perhaps the most important reason to have dependable systems is that people are coming to trust and expect that embedded computers always work. That is, if people think that systems are dependable, they may tend to use them in ways that could result in harm or loss if they in fact are not dependable. (For example, inserting an arm between elevator doors as they are slamming shut.)