I broke down and dug my 3 pasta books out, along with books by Biba Caggiano, the Frugal Gourmet (Jeff Smith), and a couple of recipes I had from Carlo Middione. Somehow I either missed this mention of using oil or dismissed it because I thought it applied to using an extruder.
From "The Pasta Gourmet - Creative Pasta Recipes from Appetizers to Desserts" by Sunny Baker and Michelle Sbraga, page 44.
"Many of the pasta directions in this book*, as well as those in the instruction booklets with the various pasta machines, call for the addition of oil to the dough. This gives the dough a silky feel, and makes cutting or extruding the dough easier. The oil can be increased by a tablespoon or two, or it can be eliminated entirely. If you adjust the amount of oil used, don't forget to also adjust the total amount of liquid used. Note that the instructions for the Cuisinart Deluxe Pasta Maker calls for oil to be added in with the flour, instead of mixing into the liquid. Olive oil is specified when it's flavor would enhance that of the pasta, while canola oil is specified when a blander oil is desired. Any other vegetable oil except olive oil can be substituted for canola."
* The truth is that very few pasta recipes in this book actually call for oil in the basic recipe (mostly limited to vegetable pastas). They give a basic recipe and then a list of Variations of the Recipe - which might include the substitution of eggs for part or all of the liquid, adding oil, etc.
Salt is another "sometimes you see it, sometimes you don't" ingredient in pasta recipes. Taken from the same source and page as above:
"The one thing we do not add to any of our pastas ... is salt. Salt has traditionally been used to both enhance flavor and preserve food. We believe that taste is better enhanced through the use of herbs and spices, and by not overcooking the food. And since you can make fresh pasta whenever you want, there is no reason to use salt as a preservative. If you must add salt, we recomment using sea salt. Keep in mind that pasta made without salt is more tender."
How many times have we seen and heard the cooking demonstrators on TV admonish us to salt the pasta cooking water because it will be the only chance we get to "season" the pasta? Obviously, as far as they are concerned, salt is not an ingredient in the pasta dough.