Look, it doesn't matter how inadequate the starter kit from Walmart is, it's CHEAP and affordable. If people want to have any enjoyments, especially as jobs are drying up, etcetera, and they want that to be fish, then they're going to go with cheap.
I live in area with a new Petco (drove the local Pets n Stuff out of business in a month), Walmart, and the new, much smaller and far more inadequate Pets n Stuff downcountry. All three carry fish, though Pets n Stuff no longer has much in the way of fish, and it's all freshies. I can totally see Walmart giving Petschmo a full run for their money, hard, and at this point they're pretty much the only games in town, especially with salties. The alternatives, should my husband or I want to set up another salt tank, would be to hit the capitol or make a three hour one-way trip to the Bay Area OR buy online. (A great deal of our shopping is done online, in fact.)
For Walmart or Petco to fail at this a couple of things would have to happen first (and that hasn't happened yet for Petco, has it?). First, there would have to be good competition. You may have or be that competition in your market, but as outlined above, there is no other real competition for these big players where I am. It can't be that uncommon, either, that relatively non-urbanized areas have little or nothing in the way of LFS competition for these players. Second, people would have to care enough, and I'll tell ya this, if they cared about Pets n Stuff, how come they immediately took their business from Pam and gave it to Petco? Price.