I think it may have been mentioned already, but feedback is voluntary. That means neither the buyer nor the seller has to leave it.So there is no should on either part. Those sellers who automatically leave feedback for buyers after the buyers leave it are doing so with eBay's blessing. As eBay provide this system, I suspect they don't have a problem with it. And buyer feedback is irrelevant.

I think the automatic feedback facility was invented to take the load off huge volume sellers who had limited time to leave feedback manually for such large number of buyers.

WHY is buyer feedback irrelevant? Well, it is at the moment where no negatives can be left for bad buyers, but otherwise?