That is a good article... Here are few others..
http://www.carbibles.com/engineoil_bible.html
"Phosphorus is the key component for valve train protection in an engine, and 1600ppm (parts per million) used to be the standard for phosphorus in engine oil. In 1996 that was dropped to 800ppm and then more recently to 400ppm - a quarter of the original spec. Valvetrains and their components are not especially cheap to replace and this drop in phosphorus content has been a problem for many engines. So why was the level dropped? Money. Next to lead, it's the second most destructive substance to shove through a catalytic converter. The US government mandated a 150,000 mile liftime on catalytic converters and the quickest way to do that was to drop phosphorous levels and bugger the valvetrain problem. Literally.
In the US, Mobil 1 originally came out with the 0W40 as a 'European Formula' as it was always above 1000 ppm. This initially got them out of the 1996 800ppm jam and knowledgeable consumers sought it out for obvious reasons. Their 15W50 has also maintained a very high level of phosphorus and all of the extended life Mobil synthetics now have at least 1000ppm. How do they get away with this? They're not classified as energy/fuel conserving oils and thus do not interfere with the precious government CAFE (corporate average fuel economy) ratings."
http://www.lnengineering.com/oil.html
Oil companies have been cutting back on the use of Zn and P as anti-wear additives, and turning to alternative zinc-free (ZF) additives and ashless dispersants since Zn, P, and sulpherated ash have been found to be bad for catalytic converters. One such ZF anti-wear additive is boron. Most of the SM and CJ-4 oils we tested contain significant concentrations of boron (B) to offset the reduction of Zn and P. The performance of these zinc-free anti-wear additives has only been proven with ultra-low sulphur fuels, not readily available in the United States with exception of new diesel fuels since 2007. Since we are discussing aircooled engines specifically, the highest levels of boron we found were in Harley Davidson’s SYN3 motor oil, which is specifically formulated for an aircooled engine, but at levels six to ten times that of what is present in any reformulated SM or CJ-4 motor oil. Additionally, Harley's SYN3 didn't reduce the Zn or P, just supplemented it with the added boron. Similarly, Swepco's 306 has high levels of boron in addition to high levels of Zn and P.
According to leading studies, Boron works best in the presence of Zn and P and may better serve to complement these anti-wear additives than as a replacement for them. This reduction is a mandate issued by API, American Petroleum Institute, who is in charge of developing standing standards for motor oils. In 1996, API introduced the API SJ classification to reduce these levels to 0.10% or less. The latest API SM standard for car oils calls for a zinc and phosphorus content less than 0.08% to reduce sulfur, carbon monoxide, and hydrocarbon emissions. As a result of this mandate, some motor oils now have as little as 0.05% zinc and phosphorus.
BTW, there seems to be a difference of opinion in what type of ZDDP is good as well..
"The two types of antiwear wear films studied, derived from zinc dialkyl dithiophosphate (alkyl ZDDP) and zinc diaryl dithiophosphate (aryl ZDDP), were chosen because they possess significantly different wear characteristics. High resolution AFM topographic images showed significant differences between the two types of films. More interestingly, high resolution imaging and quantitative mechanical properties testing using the interfacial force microscope (IFM), revealed different elastic and plastic properties between the two types of films; in addition each type of film possessed several distinct regions with respect to mechanical properties. The maximum values for elastic modulus and hardness were located on the highly loaded regions of the alkyl ZDDP films which exhibited the best tribological performance. In contrast, the aryl ZDDP films, which exhibited poorer antiwear behaviour, were devoid of such resilient regions. "
