Pointing out the fact that the most successful store in history by a huge margin is one that neither you nor anyone you know shops at is a great way to illustrate the importance of market validation for startups.
If your audience does shop at Walmart, or knows people who do, then pointing out Walmart's jaw dropping numbers will not be a good device for illuminating the importance of market validation. In fact it could encourage them carry on with the potentially mistaken assumption that the entire planet's needs/problems are the same as their own.