Here's the certifications for Rotella-T6:
HDEO qualifies for more types of service due to its more ruggedness. JASO MA for motorcycles. API-SM and higher ZDDP than other 40w oils. And one of the few with European ACEA approval, and not the old A3/B4 standard either.
Shows the issue here is some people go with quantitative measureable standards, while others fall for qualitative hearsay and I-heard/he-said/she-said type of gossip.