The cheap 2x4s are the most significant point of failure. The houses will twist and warp to many extremes during their lifetimes. The first symptom of doors that won't open/shut properly usually shows in the first 10 years of these houses. In a 1920s home built with domestic timber, that process would take a lifetime. After 30 years, this contributes to all sorts of creaks and leaks. Repairs are questionable and don't last as long because the frame of the structure is unstable.
