Well I did some looking one time and apparently the EPA found cats were degrading over time due to the ZDDP coating the platinum or some such. With Diesels going catalytic now, even Rotella had to pull the ZDDP. The NAPA 20-50 racing is supposed to have a good dose of ZDDP, By branding it racing they avoid it having to be cat compatible.
Minor point; we don't SEE oil burners "much" anymore. It's not that they aren't out there, it's just that cats finish the job and burn it up so you don't see smoke. My 05 Prius was using a quart every 2 thousand for the last 100,000 miles that's 10 gallons of oil through the cat....... Sold it at 205,000 miles and that car is doing a 100 mile a day mail route every day now, reliable as a rock.