Within reason all steam irons did the same job, some better than others but most got the job done. Also as we can see from the vast offerings at estate sales, thrifts, FleaPay etc... they tended to last the duration especially if properly cared for, so the question then becomes how to get Madame to purchase new?
Appliance makers have been onto gimmicks ever since wide spread electric use came to homes and the era of modern appliances began. Stream Lining was the first big craze and things seemed to pile up from there.
There were big irons, small irons, heavy irons, light irons, travel irons, compact irons, irons with more surface area, and so forth.
You notice that once irons started making their own steam internally without separate water tanks they began to grow in size. Compare a Westinghouse or Proctor steam iron from say the 1940's to later versions from the 1950's and 1960's. All that heft is the water tank above the soleplate. Because the more water an iron held the longer it could steam and thus save Madame trips to the faucet, the things grew to the common sizes we see today. I've got a Bernette steam iron (made in France) that holds the most water one has ever seen. About one and a half to two cups or more I reckon.