I'm no fan of Walmart (I refuse to shop there on a moral objection to Walmart's business practices), but I think that site's statistics are crap. I put in my zip code and get "...no data for Wal-Mart stores within 100 miles of 15212..." Missing from the list returned at are at least two stores that have been around for five years or more.
It seems to me that they have data on "police incidents" for certain stores in certain areas, and use it to leap to wildly inappropriate conclusions.
The "study" surveyed 551 Walmart stores out of over 3,000 in the country. No mention is made of how the stores were chosen, or of what types of communities they are located in. The "study" seems to take on a slant towards Target by comparing "police incidents" at Target stores located within ten miles. I don't know about where you live, but driving ten miles in any direction from my home I can go from ghetto to exclusive neighborhood and back to ghetto several times. Nearby, if you want to compare crime statistics, needs to be in the same shopping center to draw any reasonable conclusions.
This is a website with a clear agenda, and anyone who falls for it needs to take a few minutes and a critical mind and read through the "study".