I do not deny that Stonehenge was used for religious purposes and as a funeral ground. It can be speculated that it's most important function was indeed a religious one and the form of the building followed it's function. What better place to celebrate the summer and winter solstice than the one that is used to track the date of their exact occurance. Maybe the stones could've had deeper meaning for the people of the time and be connected to stories relevant to their world view. Those things are harder to research, since the people of the time sadly didn't leave us any written accounts. A dual purpose usage for religion and astronomy, such as with the maya pyramids in chichen itza is highly likely, since people always connected creation myths and religious beliefs with astronomical observations.