Why limited access to C: drive (Windows)?

[fergus]

Boot into Knoppix from a memory stick
mkdir /c
mount /dev/sda1 /c # /dev/sda1 is Windows system drive

Do not understand why some locations fail as in
ls -al /c/{various trajectories}
rm -vf /c/{various trajectories} # not that I'd try this!

Q1. How does Windows achieve these protected gateways that frustrate Linux access?
Q2. Can these protections be overcome?

Thank you!