Where did you get this kind of numbers? My attorney cost less then $3k and did a great job. I know a bunch of people who used him and they all got approved. I'm not saying everyone got through - I know he had some rejections as well, but that's hardly the point. And he's not the only guy on the block.
Consequently, getting an approved I-140 allowed me to take an industrial position which pays more a month than I spent on GC application. If one is not complacent and actually reads the contract he will make sure that RFE handling is included. Hence, no stimulus to bungle a case. As to Murthy - you don't really think she herself is involved in cases do you? It's a law firm with a bunch of associates doing the grunt work. Also, with all due respect to the practitioners you mentioned we have no idea how good they actually are. What we know is that they go to great lenghts to advertise and promote their services. I'm not even sure that knowing their success rate would do us any good - it's exceptionally easy to pad the score by taking only sure cases. I don't see how being known translates into being good. I mean Tonya Harding is a known figure skater.
I'm not saying there aren't valid reasons to not hire a lawyer, but the cost is not one of them. First of all, it is recouped very quickly by way of additional job opportunities. Second, it is still way cheaper than being as they put it "removed". I've seen people on this board who most probably make 3-5 times more than I did at the moment of application and still complain they have no money.
A special note about DIY kits. You realize that the people who sell them got their approvals by hiring attorneys, right?