That is possible. I was at all three recently comparing prices. BestBuy and Target had a higher ratio of 4k/1080p than Walmart but it was still less than 50/50. Was in LA recently and while I was deliberately looking, I did notice a high number of 4k displays. But then again, those are TV's. Fry's and Microcenter both still had more 1080p and 1440p monitors than 4k.
Actually
Getting back on topic, most people using Linux are not on 4k displays. It's not something the Linux dev community needs to place a big priority on. Looked into it further however and it seems 4k is well supported so the original complaint seems curious.