Yep, older machines used hot and cold fill. The difference in temperature to the desired temperature was then achieved by the element or adding cold I assume. It could be said that the older machines were more energy efficient in this regard, in terms of cost at point of use. Specifically if the hot water was heated by gas. Although the older machines probably used more water and had less low temperature options (although those in the late 80s/early 90s had 30 degrees i'm sure).
But, to make white good cheaper, the manufacturers realised they could do away with the second inlet. This had to be more robust to cope with hot water. This meant that the machine should be cheaper at point of purchase and was also cheaper to manufacturer.
So now machines come with a single inlet [cold only] and rely on the heating element to do all the work.
Personally I like the idea [in theory] of a hot water feed, especially if you have gas heating. But, I can also see the benefits of not having one. Especially, as someone mentioned above, the hot water feed is a distance from the source.
They are still standard/common in commercial machines for obvious reasons.
The Hot water can be heated locally en-mass via a gas boiler. When you are dealing with washing on that scale, gas will be a lot cheaper.
