FYI, whenever a situation like this happens where someone is under doctor's orders not to perform, it's usually a liability issue that actually keeps them from performing. An unfortunate side effect of being in a major band is that whenever you go on tour, you have a BIG insurance policy taken out in case something happens to you while you're on tour. In Chester's case, something did happen, and once he saw a doctor about it and was told he needed surgery, continuing to perform would probably void his (or more accurately, LP management's) ability to make an injury claim under their insurance policy, or even void the policy altogether, which would mean they'd be losing a TON of money, way more than they would've made back by going on with the performance.
So, in a nutshell, if you're going to be angry about this, blame it on LP's insurance company. Chester is probably physically capable of performing (he finished the Asian tour with the injury, after all), but it's really out of his control.
*Edit* I'm guessing this will probably result in Chester's appearance at that one benefit show/the rumored DBS show next month being cancelled as well.