West Coast,
We received several of the diverts from DFW during said dust storm, and I was chatting with several of their crews during slack traffic. My understanding from a couple NWA crews was that the airlines set max x-wind limits in thier ops-specs, and the max limit lowers as visibility comes down for low-vis approaches. I don't know what the RVR was at DFW at the time, but I remember hearing the vis was down to 1 1/2 mi or less for a time. I think the A319 crew said their limit was 29 knots in good vis.
V4F