Why was Silverlight 1.1 changed to Silverlight 2.0?
Previously, Microsoft had been referring to the .NET-enabled Silverlight release as “Silverlight V1.1”. After stepping back and looking at all the new features in it, they realized that calling it a point release doesn’t reflect the true nature of it. Consequently, they decided to change the name and refer to it as “Silverlight V2.0” going forward. For more details, see Scott Gu’s blog.