My counter to this, is haggling as a buyer has also become a lost art.
I no longer do haggling if I'm trying to sell something on craigslist, facebook, etc. The sheer number of people that start off with a 50% offer, planning to go up to maybe 60% is wild. Or the folks where we chat and chat and chat, agree on a price, then they show up with the "I only brought this much $$" excuse is extremely frustrating. That and you have the folks who don't even put forth the effort - they expect me to compete against myself and propose to them, a price. There's haggling, and there's just being a *****. I've yet to encounter the former, which is a real pity.
I can't speak to the business decision to discontinue the art of negotiation, but on my end: It's proven to be both a waste of time, and a slap in the face. I post something for sale with a price attached. That's what I expect to get for it. If I wanted less, then I would have posted it for less. I am not your coupon.
Perhaps I have an unpopular opinion here, but I've officially been broken by the system.