The zinc being removed for the oil back 12 or so years ago was part of a big push to rid the streets of these older cars.
Based on what I have read it isn't quite that sinister . . .
It is curious what is actually 'at work' with an engine oil's ZDDP content. It turns out that it is not the ZDDP that provides the wear protection but the deposits left by the thermal break down of the zinc phosphate -
Ferguson, Johnson, Gonzales, Hobbs, Allen and Williams The problem with the deposits is that they also accumulate on the surfaces of the catalytic converter - causing the unit to become less and less efficient - eventually failing emissions testing. So ZDDP levels have been declining in response to effect on emissions equipment (on which the government mandates extra-long warranties from the auto makers).
