Okay, let's give this some thought about Rotors.

They are made out of steel (not iron). Steel is an alloy of iron and
carbon (often times with a few other miscellaneous additives). Steel
(and Iron) will oxidize (rust), given exposure to Oxygen. Certain
factors will accelarate this rusting such as salt.

What can be done to minimize this rusting? Well the typical solutions
are to coat the material so as to prevent exposure to Oxygen. This is
impractical (paint) or unsafe (oil/grease) with brake rotors. Brake
rotors are an ablative surface...i.e. it intentionally wears as it is
used. This removes the rust from the wear surface. it does nothing on
the other surfaces.

Other ways to prevent rusting are to make the rotor out of non-rusting
materials. Stainless steel is not a good choice as it's thermal
characterics are horrible (it would warp or crack far too quickly.)
Porsche has ceramic rotors. Incredibly expensive. Also somewhat
fragile.

Eric says his rotors are poorly manufactured. Most listees with
experience find this a doubtful statement. It is not impossible
however. Until or unless there is photographic evidence and micrometer
measurements to support this, the rest of us will likely never know.