Sam's Club's Got A Plastic Problem

I have determined that Sam's Club is EVIL. I signed up for a membership yesterday and bought a membershipt. While going through the membership signup the guy says "Kevin, you've been pre-approved for a Sam's Club Credit Card. Would you like to accept the offer, decline the offer or deal with it at a later date?" I told the guy that I didn't want a credit card and that I would be on my merry little way. He told me that since I was going to be shopping at the club that day, that I could just pay for my membership when I checked out at the register. About 45 minutes later when I get to the register, the cashier gives me my total and tells my that my credit card can't be used at Sam's Club. Now, I'd be fine with it if it was an American Express or JCB or Diner's Club or something obscure like that. IT'S A VISA. How do you not take VISA? That's like not taking cash. So I find out the hard way that Sam's only takes the Sam's Club Card, the Wal-Mart Card and DISCOVER. Now, this is what floored me. DISCOVER!? Who the HELL carries a Discover card? I sure as hell can't even GET a Discover card and in my 2 years of retail have never seen more than two on any given day. NOT THAT POPULAR A CARD but VISA!? Come ON people. I have a feeling that the only reason Sam's even takes the Discover is because of the co-branded Sam's Club Discover Card. You can't not take the Sam's Club Discover AT Sam's Club. This is complete and utter bullshit. I've bought multiple items on Sam's website with my mom's membership with what but Mastercard or Visa. So my question to anyone out there is why Sam's only takes their own cards in the store but will take anyting online. Better yet, why are we allowed to use cash if it isn't tied to Sam Walton in some form or another?