I'm a home inspector and an investor. I can tell you that PB can actually be a nightmare and has been for many people in the past, which is why builders don't use it any longer. I can also tell you that many home inspectors make things way worse than what they are, because of the liability or the fact that they don't actually do their homework. Home inspections are meant to inform the buyer, not scare them. The inspection should give them leverage to re-negotiate and get a better deal if need be, or simply walk away if it's too much for that client. Home inspections came about as a consumer protection method, and we are supposed to be objective and informative. PB was used for decades because of the cost, and like with many things, you pay for what you get. PB has been found to have its structural integrity reduced compared to other materials because of the way many chemicals in public water supplies react to it, breaking it down and causing small cracks over a long period of time. This means that at any given time, pipes can fail and sometimes several can all at the same time which is where this inspector was probably getting at. It's pretty tough to tell exactly when a failing pipe will happen with PB. If it were me, I would just budget to replace them eventually with PEX. Try to get yourself a better deal because of it though.
Just my two cents...