What we’re trying to do with Flash is create a feature-rich run time that’s consistent across all of the platforms. That’s something that has not been the reality for other web technologies. Browsers have not been consistent - even the Java Virtual Machine is rarely consistent on different platforms. For the past 10 years, we’ve been able to say, ‘Here is a technology and a set of tools that allow you to create content once, then deliver it to a wide variety of platforms and know that it’s going to work consistently.’

Quote from Mike Downey in Wired via JD