Where in there does he, or the link he references, substantiate the following claim?

  The broadcast industry does not want American's to know
  this, but they are legally obligated to provide the free
  "over the air" stations on cable (coax) even if you do not
  pay for cable service.

If you follow the link trail, you'll find this quote from the FCC:

  broadcast signals that are subject to mandatory carriage
  must be "viewable via cable on all television receivers of
  a subscriber which are connected to a cable system by a
  cable operator or for which a cable operator provides a
  connection."

Which is another way of saying what I wrote above. Bottom line is: if you aren't paying for cable video service and receiving these channels, you're benefiting from the cable company not wanting to send out a tech to install a filter, not some legal requirement.

I'm not trying to win a legal case here, just sayin'... 1. "The broadcast industry does not want American's to know..." Opinion. Why would they want this widely known? 2. "...legally obligated..." OK, that might be a little strong, but I stand by the POV that they can not encrypt this signal. The FCC citations (on Engadget article) make that clear (to me).

It's possible that this works for me (and others) because... I am a subscriber to my cable company for telephone and internet access (but not TV), and so they can not send a tech out to disconnect me from their grid because it would terminate my current services AND they can not encrypt the Clear QAM signal for the Broadcast TV channels.

Again, I'm not trying to argue some legal case here. But I do think it's more than just the cable company being lazy and not sending a technician out.

  I'm not trying to win a legal case here, just sayin'... 1.
  "The broadcast industry does not want American's to
  know..." Opinion. Why would they want this widely known?
  2. "...legally obligated..." OK, that might be a little
  strong, but I stand by the POV that they can not encrypt
  this signal. The FCC citations (on Engadget article) make
  that clear (to me).

Agree. Sorry if I'm being pedantic, but this is really nothing more than the cable companies being compelled to broadcast these "mandatory carriage" channels without encryption and the impracticality of filtering every non-subscriber.

  It's possible that this works for me (and others)
  because... I am a subscriber to my cable company for
  telephone and internet access (but not TV), and so they
  can not send a tech out to disconnect me from their grid
  because it would terminate my current services[...]

That's why it works; however, it's not so much that they can't disconnect you but that they can't practically filter you.

  [...] AND they can not encrypt the Clear QAM signal for
  the Broadcast TV channels.

They can't encrypt but they can filter non-subscribers. If this were always practical, there's no doubt many companies would aggressively filter.

  Again, I'm not trying to argue some legal case here. But I
  do think it's more than just the cable company being lazy
  and not sending a technician out.

Sure, the impracticality is there but no legal impediments that I know of :)

My understanding is that it's more subtle than that. If you subscribe to no TV services, they can block all channels. However, if you get any TV service from your provider, they have to provide all broadcast channels to you, either un-encrypted, or encrypted with a free cable box for every TV in your house.