Dude, this is an excellent post that refutes their typical fallback argument that "it is silly to think only east-aftricans are doping if doping is available". As you have eloquently laid it out, the point is that it just happens to be more convenient to dope in east-africa, and escape detection much more easily than in the west, for a number of reasons. One additional point to add to your list is that very talented young prodigies can be cheaply hidden away in camps for years, while being trained, while building the blood with the aid of PED's, for a number of years before they then burst upon the scene to quickly set records (at which time they enter the bio-passport program) (or they try to cheat the bio-passport program initially by taking on a falsified passport, with falsified age and falsified name).
In the west, the prodigies, like a Mary Cain, cannot be hidden away for a number of years to escape the doping checks, because after turning pro, the public/sponsor will expect racing.