Having been in the commercial and industrial laundry industry for more years than I care to admit, I have to say that CyanoticWasp’s comparison of a bath/shower to front-loader/top-loader machines is spot on and not a description I have ever heard. Bravo!
@Lightlyseared: Tumbling allows for what is called “mechanical action” on the clothes and allows for better cleaning. Essentially, the clothes are raised up to the top of the drum and then they drop down onto the other clothes and water at the bottom. This action causes disturbance to the fibers and helps loosen soil. Agitation pulls clothes through the water and there is very little mechanical action and also leads to the need for more water.
Lastly, the more efficient machines need to run longer because of the simple truth that you need three things to clean linen: Time. Temperature. Product (detergent/water/bleach et cetera). If you have less of one you need more of another. Therefore, less detergent, water, and in the case of some super efficient models, temperature means you will need more time to get the job done.