Over my dead (gorgeous) body.

[Eruanna]

You are nothing if not definite in your observations Burrahobbit! That's it? End of discussion?

narfforc said:

I think a lot of what Tolkien wrote about burial mounds comes from myth and folklore. The ancients worshiped such places as entrances to the underworld.

In Icelandic, Scandanavian, Celtic and Ancient British folklore (among others) there are also tales that have burial mounds being places where one could enter the Land of Faerie. Perhaps it is simply that Professor Tolkien was influenced by these ideas and tales when he wished to emphasise the tragic deaths of those interred in the mounds.
As far as I understand it, barrows and burial mounds are also said to be particularly strong in magnetic and or magical influence as they are often constructed at the meeting points of ley lines. I don't know much about ley lines and such, so I would not like to dismiss the idea out of hand.