IME, most installations where Hadoop is "successfully" used it's running on pretty high-end machines. "Commodity hardware" really means standard hardware, not cheap hardware (as opposed to buying proprietary appliances and mainframes).
I'm not sure what your point is with a hypothetical situation. Why wouldn't the be able to query their data? All I'm saying is from my actual experience with real users, it's best to build a Hadoop cluster with high quality hardware if you can.
