well, the registry has types. files are raw binary data that is almost entirely untyped. how could they possibly enforce typed data without diverging from the filesystem metaphor?
Cmdlets can have provider-specific parameters, so in this case I would add a registry-provider-specific data type parameter with sensible default behavior to New-Item and Set-Content.
For example...
Set-Content hklm:\software\xyz\abc -value 1
...could create a DWORD value by default based on the type of the value argument, while adding '-DataType String' would enable creating a string value.
Files are raw binary data, but a (BTW unreliable) method to understand what they contain has been in use since years: file extensions.
I can see no reason why in a filesystem-like representation of the Registry you cannot have a value.dwd (which is a DWORD), a value.bin (which is a BINary), value.esz, etc., or at least that is what I would use.
For example...
Set-Content hklm:\software\xyz\abc -value 1
...could create a DWORD value by default based on the type of the value argument, while adding '-DataType String' would enable creating a string value.