What is in Silverlight 1 that is not in Silverlight 2?
Nothing. Silverlight 2 is a full superset of Silverlight 1.0. It is 100% compatible with Silverlight 1.0 applications and provides more powerful features and functionality. Silverlight 1.0 applications even benefit from improvements in media playback and performance characteristics of Silverlight 2 without any additional changes needed.