A low seat height is the central, probably most important element of the cruiser style and many other elements of the cruiser style were developed because of the low seat height. For example, the narrow engine, the foot forward riding position, the speedometer on the gas tank, and the small diameter rear wheel all work well with the low seat height.
Many people get really confused about "Cruiser style" and "Harley Davidson style", thinking that we only use the word cruiser because we are not allowed to call it Harley Davidson due to trade mark infringements. Kind of like the situation where you can't call a photocopier a "Xerox machine" any more.OK let's stop that idea here and now. Cruiser style is not merely a politically correct way of saying Harley Davidson style. However, I will admit that Harley Davidson may have pushed the cruiser style more than most. And many, if not most cruiser style bikes, do mimic the appearance of a Harley Davidson.
Some people also think that cruiser style is another word for "Retro American" style. Also not true. The cruiser style is a design that has emerged since the mid seventies. Harley Davidson style has existed since the twenties and thirties if not more. The cruiser does not go back to the pre-war era in America. If you will take a closer look at the old 1930 motorcycles, they were set up with higher seats, and the foot positions were relatively further back.
The importance of the cruiser style is that it has made motorcycles accessible to shorter people, just the way that the electric start has made motorcycles available to people who have trouble in kick starting an engine over. The two trends kind of worked together and emerged at about the same time. Today, more women ride motorcycles, and more older people ride motorcycles because they are not as intimidating as they used to be in the thirties.
Just take a look at Harley Davidson from the sixties and compare them to recent models, and you will see there a general lowering of seat heights and a moving forward of the foot controls.
So even if we didn't use the word "cruiser" for lower seat heights and more forward foot positions, we should make up a word for it, and keep it distinct from Harley Davidson style. It is a trend in motorcycle style, and exists for real reasons that have nothing to do with any particular brand.
Another (contrary) view of cruiser style: http://www.flamesonmytank.co.za/Cruiser.htm
Check out this web page with the history of the sportster. Notice the gradual lowering of the seat, the moving forward of the foot pegs and the fattening of the ever smaller diameter rear tires.
Pictures: http://www.sportster.org/history/