"As far as setting hardware registers and such goes, C allows access just like assembler."

Not really.
The ANSI (or K&R) standard 'C' language provides no specific facilities to address hardware registers. This almost invariably requires some compiler- and target-specific extensions to the language; eg, in Keil you have the extended keywords like sfr, xdata, bit, etc
Borland compilers used to provide special extensions to allow access to the x86's IO Port address space.

Another area where extensions are usually required is in the handling of interrupts.