I have a feeling you're less likely to have a company try to pull something on you when it's a very large company, especially one that operates in multiple states. That's likely because there might be a state where the law is a bit more specific and clear cut and having to deal with the resulting PR disaster from a case being brought pretty quickly overshadows most the money that might have been saved.

Additionally, Walmart in particular is no stranger to class-action suits brought from it's employees. Given how little Walmart pays the average employee and how profitable it is, this behavior would have a very little and well bounded guaranteed upside (saved money), but a large unknown possible downside (lawsuits, bad PR, etc). When profits are good, that risk reward ratio probably just doesn't look very worthwhile to most companies.