I don't recall who wrote:
"Clearly, once one has used a frame for brood, it can no longer be used
 in honey supers."

Simply not so.  Many operations switch brood and honey frames, a practice
that is far more common than it should be.  There are reasons why one would
not want to do this.  Someone pointed out that honey may become tainted with
cocoon taste.  I'm not sure if this is so, but suppose it's possible.  Combs
that have been used for brooding are susceptible to wax moth invasion
whereas comb used strictly for honey production is of minimal interest to
wax moths.  The most compelling reason to segregate honey comb from brood
comb is the possibility of chemical contamination.  Combs that have been
exposed to everything including the kitchen sink have no place in honey
supers.

Having said all that, I repeat that it is not uncommon for some operations
to interchange frames from brood to honey supers or vice versa.  At some
point relative to size of the operation, the time required to keep things
separate outweighs the reasons to do so.

Aaron Morris - thinking separate and not equal.