The Walmart "problem" is they are trying to get out of credit card fees, which is why they have disabled NFC. While Apple made a big deal of "partners" the reality is that their partners have been entities that were accepting NFC (and so took Google Wallet as well). They have their system they want buyers to use instead (CurrentC) which would involve use of bar codes tied directly to your bank account, but so far it's been "stuck" in limited beta forever.
CurrentC had an exclusivity agreement with a number of vendors, but many of those chose to ignore it (Circle K was listed as a CurrentC partner, but the NFC has always worked) and now the agreements reportedly have expired. Ignoring the exclusivity agreement became the norm after Rite Aid and CVS took heat for disabling NFC right after Apple Pay was released (which also killed Google Wallet that had been working there for years).
Would be interesting to see if Walmart has figured out a way to block Samsung Pay short of no longer taking Visa or Mastercard. Not using NFC, it seems the only way to block it would be to stop accepting card swiping, which right now isn't feasible. That may not be true in a year or so, but I don't think anyone will care about CurrentC by then.