We don’t think there’s any one answer – ask a dozen chefs and you’re likely to come up with at least a number of answers. Both Professional Cooking by Wayne Gisslen and The Professional Chef from the Culinary Institute of America refer to sautéing vegetables in butter or oil, not stock.
Depending on the vegetable, it may be blanched before sautéeing – green beans, carrots, potatoes and other dense vegetables are generally blanched to cut down on the final cooking time. Zucchini, summer squash, mushrooms and other less dense vegetables generally are not blanched.
There is a trend cropping up in cookbooks here and there of recommending that people “fry” vegetables and other foods in stock in the ever-broadening effort to cut fat from people’s diets. It is possible that this method of cooking (really a type of braising) is finding greater acceptance in restaurant kitchens, as well. Generally in this case, the vegetables are served in their cooking sauce.