You wrote (in your blog),
"... the basic formulation of soap hasn't changed much since our ancestors rendered down bear fat in huge kettles and mixed it with fireplace ashes to form gray bars of caustic glycerine."
Not quite. Fat is basically a compound (an ester) of glycerine with any of various fatty acids (carboxylic acids). Soap is the sodium salt of the fatty acid part. The glycerine moiety of fats is not even always part of in the final product. [what about glycerine soaps?]
More than that, most laundry detergents are not made from fats or plant oils at all, but are sodium salts of sulfonic acids rather than fatty acids. (Somewhat better performance, especially in water with a high calcium content (“hard water”).)
There are a few actual laundry soaps still on the market — Fels Naptha, Ivory Snow. (Ivory brand bar soap was originally created as a laundry soap.) BTW, I’ve tried Fels Naptha just for the heck of it, and it does the job, but is a bit less convenient to use, as it needs to be dissolved first.
Most bath soaps are actual soaps, as they are milder on the skin than sulfonic acid detergents or other degreasers. (Ivory soap is actually very harsh and alkaline as bath soaps go, as, again, it was originally a laundry soap.)
However, your basic idea, that detergent is a relatively cheap product with little to distinguish the high-end brands, is probably mostly correct.
I have noted myself also that a smaller amount than recommended, as little as 1/8 of a cup by volume, of powdered detergent does as good a job as more does, on all but very heavily soiled clothes. For stains, the detergent for the entire load, can be applied directly to the stained part (as in those 1960s Whisk (TM) ads). I’ve also found that soaking clothes (either in a bucket, or just in the washing machine with the cycle interrupted) makes them come out a little cleaner. The washing machine spends most of its time sitting idle anyway!
All good points, if not a bit technical for me. I have a bar of Fels Naptha as a friend says it is good for spot stain removal. Sometimes the old ways are best.