According to Valvoline's product info pdf,
http://www.valvoline.com/pdf/premium_conventional.pdf, 10w40 and 20w50 have the same amounts of zinc and phosphorous as the other grades, 5w20, 5w30, 10w30.
The only oils they offer with increased amounts is VR1 and Motorcycle oil.
The product info pdf is readily available for download for each type of oil Valvoline offer. They don't say zddp, only zinc / phosphorus, which I take to be synonymous, isn't that correct?
I read through the documentation from the American Petroluem Institute, a while back. I cannot find what I read on the website now, though. Do you have it, Ted? The way I interpreted it is that 40w and higher, 10w40, 20w50, etc. and single viscosity oils don't have to have the reduced amount but I also don't recall anything that said they have to have higher amounts. It seems to be up to the motor oil company as to how they want to handle it.
Lawrenceville, GA