Why do publishers/authors come out with new, updated cookbooks? Are the new ones better or are the old ones still preferred? The answers to those questions are "it depends."
For the first question as to why publishers and authors reinvent the wheel every so often and publish a new edition, there are several reasons.
- Money: Let's be honest here, folks. If a new edition will sell better or more copies than an old one, if it will bring back to the public's mind a forgotten gem, then you can be sure they'll reissue it as new and improved. Sometimes that backfires. The jury's divided on the 1997 edition of Joy because of all the chapters the editors took out. Thus the new Joy claims to have put those back in; but 1997 fans complain that some of the valuable '97 stuff was taken back out.
- Ingredients Change: Old cookbooks are so much fun to look at. But, try to bake some bread by an old recipe. Odds are, the bread will be difficult to make. Flours have changed over the years, yeast no longer comes in cake form, machines are available to speed things along or to knead more efficiently, and so forth. Boneless, skinless cuts of meat are widely available and relatively inexpensive; they don't appear at all in most cookbooks published before 1980. In contrast, you're likely to find more processed ingredients and "shortcuts" in newer cookbooks (even spaghetti sauce, salsa, and frozen vegetables weren't the norm back in the day).
- Diets Change: Many of my "all-purpose" cookbooks were published in the late 1990's. Sodium and fat were the buzzwords. As a result, many of those recipes are low in sodium and have low-fat strategies listed or even presented as the ideal recipe. Margarine and shortening make frequent appearances; nowadays, butter is back as king of fat sources in baked goods because we now know of the evils of trans fats.
- People Change: Most Americans now want a little ethnic splash in with their meat and potatoes. Many Americans are trying to cut back on meat and beef up their vegetable intake. In older cookbooks, say from 1980 on back, the vegetable chapters are largely casserole- or doctored up- treatments of the few vegetables available then. Mexican flavors are scanty, Thai doesn't exist, and the few Indian or Chinese dishes are quite predictable in flavor. We have more ingredients available now, and we want to eat differently now.
- Background Knowledge Changes: In the really old cookbooks (say, before 1940), there is very little guidance in the cooking realm. Directions are sparse: fry the chicken in a bit of hot fat in a hot skillet. We, who grew up on much more precise cookbook fare, want to know how big a pan? how much oil? what type of oil is best? what temperature should the oil be? how long do we fry the chicken? I suspect those cooking for their families in the early 20th century entered the kitchen with better background knowledge, if only because their mothers/cooks cooked fairly similar meals and they got to watch the process over and over and over.
If you want to really cook from scratch, check out older versions of cookbooks or look for some of the newer cookbooks that include recipes for salsa, chutney, cream sauce, and ketchup along with their roast chicken.