I think because Neiman Marcus one of the top upscale department stores, they don't really have to price match. The "NM customer" isn't really concerned with the lowest price as much as selection, exclusivity and the fact they like shopping at NM.
For a while, I had a long stretch where I refused to buy anything from NM because I received poor customer service there. Especially at the STL location. I'm not talking about usual complaints we read where people expected more "service"... I'm talking, extremely rude behavior. One SA refused to go in the back and get shoes for me to try on and told me to try on the floor model instead! So I'm not too much of a NM fan. I love Cusp (their concept store) and BG though!
But my MIL LOOOOOVES NM. She doesn't really care to comparison shop at different department stores. She just knows that if she walks into a NM, she'll find something she likes. She likes being InCircle. She likes how they gift wrap and put charms/gifts dangling off their gift ribbon... and she knows they only sell the best at Neiman Marcus.