Europe vs Japan

Japanese engines' (say rb26dett) output is often wound up to 1000 hp and more, which is 3-5 times the stock output. At the same time, European cars' engines output after tuner's interference (guys like Brabus, Carlsson, Hammann, AC Schnitzer, ABT) increases by humble 30, rarely 50 percent. I mean I've never heard of a 1500 hp SL600 or M5. Why is that, what's so wrong with German engines? Is it because European tuners prefer to avoid inclined damage to the engine? Then what about damage to 2,6 litre rb26dett producing 1300 hp? I guess a 6 litre Merc engine would suffer less at the same output. Or is it because euro motors have some inherent problem with being turbocharged?