Most business care about paying customer and don't want to wast money on others no?
As mentioned on AdWords FAQ, ROI is simple to compute : (Revenue - Cost) / Cost = ROI.
Why AdWords nor Google Analytics doesn't allow you to PProiC easily (Pay Per ROI Click)?
Because you are selling a brand, cost is hard to measure, we can't measure the exact ROI, blablabla....
The truth is that if most companies were able to measure real PPC easily, they will stop using standard PPC because its simply too expensive. Let's take an example: 1$/click, 8266 clicks, 39 sales -> 211.95$/sales. If your average sales is 150$/click, you are loosing 61.95$/click and need to pump more money into your business?
Why do you think so many companies are doing email marketing with mailchimp or marketo or try to optimize their campaigns with acquisio? They want positive ROI/limit the dilution of their marging and are just desperately looking for PPC alternative like ROI dashboard but who can compete free Google Analytics, QMining?
PPC are great solutions to increase sales but also a powerful tool to kill many companies who are looking for better tool to reach their audience. Google has to be disrupted but who is strong enough to take that challenge...
Why Google might never move to PProiC? Because it will never go against its core business model, would you? no one does until they face the wall like Microsoft did last month.