Silverlight 1.1 is no more ... Microsoft decided when looking at the new Silverlight software that a minor version upgrade would not show the value of the product. So, from now on the next version of Silverlight will be referred to as being Silverlight 2.0. No more minor improvements, Silverlight 2.0 will show big changes compared to 1.0.

Here you can read all about it:
http://blogs.msdn.com/tims/archive/2007/11/29/silverlight-1-1-is-now-silverlight-2-0.aspx