You are correct, if you are paying for insurance from BCBS, and other providers, you should be able to get the "perks" that go with having your prescription filled at a pharmacy of your choosing.
I think Target (and others) are referring to prescription programs that are known by the public to be federally-funded, such as Medicare/Medicaid (for seniors/low income families), and Tricare (U.S. Military).
OTOH, if you happen to live in NY/NJ, you won't be able to take advantage of any of these offers -- in other words, fuhgettaboutit...