Probably a few little items like DOHC, 4 valves per cylinder, variable valve timing, EFI, variable intake volume, and let's not forget computer control to make it all work...
Ding Ding!! Winner. My 5.7 hemi does almost exactly as you say, idles smooth, runs great, lots of power and hopefully some economy too. The base of the 318/360 is still "old technology" so although there are great parts avail these days for power/performance and driveability we are still adapting these parts to a much older product, and topping it off with a very low tech distributor and carb...