80% of my flying is on CSA and I've never come across the R booking class. UW (only direct flts) and SG (all flts) normally are the 4 cheapest classes. They had been intended to be at LCC levels before oil prices shot up and OK decided to go with the flow and add fuel surcharges that make these "cheap" tix significantly less cheap (esp. if you're on a 4+ segment ticket). OK+ only gives 50% credit for them.
Never seen an R fare on AZ, either, but I 'm no expert on their policies.