It's true that a nearby 50 kW AM station can severely affect most ham receivers. However, this is often due to an inherent design defect--modern receivers with DC to daylight coverage typically rely heavily on low pass filtering, with some help from wide bandpass filtering. This is a cost tradeoff--it just isn't practical to put tight bandpass filtering and cover the entire HF spectrum. There are a few exceptions--the Elecraft K2 has tight bandpass filtering--but doesn't have a general coverage receiver. Another example is the Ten Tec Orion, which also covers just the ham bands. One option is to buy external bandpass filters--they are sold by Top Ten Devices and Dunestar for multi-transmitter contest stations. Below are published articles on building tight bandpass filters.