Get-ChildItem vs. direct use of the .NET Framework's [System.IO.Directory]::GetFiles() method with UNC paths

When using a UNC path (ex: \\machine\share\dir), I can get a file list when using the dir command (Get-ChildItem) from a UNC path, but if I try [System.IO.Directory]::GetFiles, I get an empty list (not an error, just no items). I thought that PS was built on the .NET framework. Does anyone know why Get-ChildItem would work with a UNC path while the .NET GetFiles method returns an empty list?