Is GHC required to be installed on the target OS I compile Haskell binaries for in order for these binaries to run? I need a quick answer on that!

Nope! As long as they're compiled for the right architecture, GHC-produced binaries should run anywhere, whether GHC is there or not. This is true for any compiler that produces native binaries (as opposed to certain languages which require a virtual machine...)

By the way there is no computer in the 4 or so networks I have online access to on which ghc is not installed, which might be a sign

people like haskell here in Heidelberg/Mannheim, Germany.

Cool! =) It's probably also a sign of the great work various people have done packaging GHC for various package systems.

-Brent