Policy files which redirect applications to newer versions of ESRI assemblies are no longer distributed with ArcGIS since 10.0.
I cannot comment on the 10.1 beta specifically as I do not have it installed, but my understanding is that ESRI no longer distributes these policy files so that developers are forced to test (and recompile) their customizations on the new release. Maybe final 10.1 will include policy files which would allow redirecting 10.0 assembly references to 10.1.
If you are developing a standalone application, you can specify assembly redirects yourself in its configuration file. For ArcMap, you would need to add the redirect configuration in ArcMap.exe.config placed besides ArcMap.exe.
Also, be aware of a common misconception: lots of people seem to believe that the "Specific version" switch for an assembly reference in Visual Studio has any runtime effect. It affects VS only, not the resulting compiled assembly behavior.