True enough about the different internals of the AK and Sturmgewehr 44. The resemblance is really only in concept and physical appearance. However, Hugo Schmeisser, the primary designer of the StG44, was relocated after capture to Izhevsk to work for the Red Army on firearms design. I've sometimes wondered if he had any input to the design of the AK. There appears to be very little hard information about his time in the USSR, but whether that is just general Soviet secretiveness or an attempt to obscure his contributions to Soviet small arms design, whether great or small, I don't know.
As for the reliability of the AK, I believe that can be traced to its bolt overtravel, oversized gas system, and loose clearances (not tolerances) in the various internal mechanisms, all deliberately designed into the AK, by someone who knew that the quality of materials and manufacturing would not be the highest, the training of the users not the best, and conditions under which it was fielded (both environmental and logistic) not the most favorable. A pretty well-engineered firearm, I'd say.