Why don't most non-East Asian varieties of rice stick together? Having tried a number of different kinds of rice, I've noticed that the only ones that seem to have grains that "stick" together are white varieties often used in East Asian cooking (jasmine (to some extent), Calrose and other "Japanese" types, etc.). (Glutinous rice also has this property, albeit to a much more pronounced extent, for obvious reasons.)

Conversely, a lot of other types don't (at least not to the same extent, and when they're not overcooked). For instance, the rice often served at Middle Eastern restaurants doesn't "stick". Nor do basmati or red/brown varieties. I've also had mixed experiences with white rice of the American long-grain variety, although there's the possibility that the place that was serving me it was undercooking it.

For what it counts, the only types of rice I've had experience cooking with (either stove-top or in a rice-cooker) are jasmine, Calrose, and red and brown varieties. I rinse my rice, but would not know if the rice I've had in restaurants or other types of eateries has been, and I'm not sure if this might result in a difference.

Thus: why is there such a difference in "stickiness", in terms of chemical/physical differences? Are there also differences in preparation (e.g. washing rice) that might affect things?
Please see the excerpt below from  this page . There is also a chart that lists different types of long, medium, and short grain rices and their characteristics and usage examples.


  Rice is composed of two different types of starch molecules: amylose and amylopectin. The amounts of these two starches determine the texture of rice when it is cooked.
  
  Rice with higher amylose content, such as long grain rice, is firmer and fluffier. Rice with lower amylose content, such as short and medium grain rice, has a softer, stickier texture.
  
  The Effect of Starch on Rice Cooking:
  
  
  Dishes such as risotto and sushi rely on rice that is low in amylose to create their characteristic soft and sticky textures.
  Rice dishes that have fluffy separate grains, like rice pilaf, are best made with rice that is higher in amylose starch.
  Some sticky rice dishes, like many Asian desserts, are made from varieties of rice that contain no amylose starch. These varieties of rice are called sweet, waxy or glutinous rice.
  


In general, the shorter the grain, the stickier the rice will be.