You've probably opened a reference assembly. Reference assemblies are hollow assemblies, containing only the signatures of the types and all their members of the real assemblies they "reference". They're used by various tools in the development process to represent their "full" equivalents. Thus, the "real" assembly and the "hollow" one have the same strong names and can be easily mistaken. If you want to see the code in the methods, you need to open the "real" assembly. Since the example you've given is essentially the Silverlight's mscorlib, the path to the "real" Silverlight assembly is %Program Files%\ Microsoft Silverlight\ <Version>.
I hope this will solve your problem.
the Telerik team