Gacutil shows the content of ngen cache in v1.0 and v1.1. In v2.0, this feature is removed from gacutil.
The reason is several folds:
1. We want people to use the right tool for the right job. Ngen.exe is the right tool to managed ngen cache. Gacutil should only managed GAC.
2. Ngen is re-designed in v2.0. It is way beyond Gacutil's ability to managed ngen cache. This is quite obvious if you compare ngen.exe in v1.1 and in v2.0.
Please use ngen.exe for ngen assemblies related features.