why cremate?

In many of the Dharmic faiths particularly Hinduism it's common to cremate the body of the deceased once they have passed away. I Know that fire is considered sacred but I've never really gone into any depth to learn why it's important to cremate the body once someone has passed on. So after doing quite a bit of searching and not coming up with anything more then how the ritual is performed by who and when, typically it's performed by the closest relative of the deceased and must be performed within 6 days of the deceased's passing, the only exceptions being priests and infants; interestingly priests are buried in the lotus position. So why cremate? well I came across a few pages that sort of gave an explanation and here is my interpretation of what I've learned, it all goes back to the idea of the soul being something separate from the body and with each reincarnation the soul uses the body as a shell to take the form once the previous body has passed on. When a person dies, and the body is cremated the body is no longer sacred since the soul has left the body to be reincarnated into another life-form. Another reason, mostly from Hindu culture, is that by cremating the body that the soul once occupied, it helps the soul to release any attachment it may hold to the body in which it was a part and helps to transition the soul into it's next life, or eventually to Moksh, the eternal liberation of the soul from having to recur into a new life. Quite interesting. Now to start learning about why the rituals upon death came about in othe religions, mainly the Abrahamic ones.

Sources:
http://www.deathonline.net/disposal/cremation/hindu.cfm
http://www.learnnc.org/lp/multimedia/4281
http://www.giftofireland.com/Religionandcremation.htm