Why rinse basmati rice? Every Indian recipe I see seems to insist on rinsing basmati rice before cooking it. Why, I have no idea, because I never rinse it, yet I can discern no difference between my rice and rice cooked by other people that have, presumably, spent the extra 15 minutes rinsing. 

If the stickiness is the difference, as suggested in this thread, then I would suggest that not rinsing the rice would make eating rice-based thali a lot less traumatic because the grains would clump together more easily.
I am wondering if the origin of this step in the recipe comes from recipes written in India, and have been copied over into western book without asking this questions.

I do know that many times in India, rice is stored in sacks with some kind of insecticide (usually boric acid) applied to it. So there's always a need to wash the rice before it's cooked.. So maybe this step comes from that..