The metric quantities are from the original recipe and have been loosely translated. There is little to be gained by maintaining needless precision. Given the variations in the quality and characteristics of ingredients, there is a lot of slack in these recipes, so we may as well keep quantities easy to measure and then adjust to taste.
While many Americans worry about the introduction of the metric system and its impact on our food supply, we worry about the introduction of product code numbers, particularly at the supermarket. This is a major problem when buying vegetables with which the check out person is unfamiliar. If you don't remember the code number and it isn't actually on the vegetable, you have a problem. So, after a bit, one learns that radiccio is 555 at one store and that yucca root is 436 (9436 for organic) at another.
The next logical step is to get rid of vegetable names completely as they can really get confusing. Is it coriander, cilantro or Chinese parsley? Isn't it easier to just say "712"? We can imagine the cookbook of the future listing ingredients as:
We have seen the future.
