I am currently working through the King Schools IFR DVDs in
preparation for my US IFR written. Something is really bugging me,
and I figured someone here might know the answer.... (And I am too
impatient to wait for my next lesson.)

In one section of this course, we learn that the outer merker and
middle marker used to matter. It used to be the case that if they
were broken you had to increase your approach minimums by some amount.
But the King's don't think we have to know why your minimums used to
change, how the rule about minimums changed (other than getting
abolished), or why the rule changed -- simply that it no longer
matters any more, and you must know that since some FAA questions will
try to "trick" you by giving you the old rules (which I don't know
anyways) as potential answers.

They then go and devote a whole section of the course to suitable
substitutions for the broken devices. So now I know that if I want to
ignore the outer marker on an ILS, and it happens to be broken, it is
legal for me to substitute an NDB and ignore that instead.

So my question is twofold:

a) are marker beacons used for any real (regulatory) purpose any more,
or are they simply for positional awareness?

b) if the answer to (a) is "no, they are no longer used", why do we
have to memorize a set of rules about what we can legally substitute
for these unused beacons?

Chris