We had this discussion on here just a week or two ago.
The front sprocket rotates approx 3 times in relation to the back sprocket once, the load/strain is shared out over more teeth on the rear as opposed to the small front, hence less wear on the rear.
IE: More rotation more wear (A small tyre rotating at a set road speed will wear out much quicker than a tyre 3 times the size at that same set road speed, that's my understanding on sprocket wear.
Its the front sprocket that pulls the chain and wears the chain out, which in turn shags the rear sprocket. The most worn (Front Sprocket) part wears the following parts,
I had this conversation with someone on here and we agreed that the front sprocket wears 3 times faster than the rear, the front is taking the first stain of the toque from the engine the rear just does as it told and follows the front. The worn front sprocket wears the chain which wears out the rear sprocket, change the front sprocket more often and your chain will last longer as will the rear sprocket, you can get front sprocket on evilBay for 6 or 7 quid, full chain set just a shed load more.
I will try and find the post that it was discussed in, someone in that post put it more succinctly than I.