it seems that for someone to become the master of the elder wand he has to beat(not kill)the previous owner of the wand,and the fact that Malfoy had never even touched the wand is unimportant because it is the owner you must beat.

About why Harry survived,he had a piece of Voldy's soul in him.For the Horcrux to be destroyed if it is completely unrelated to the host,the host can remain intact...

i hope i helped..