New VS Old 340 6-pack

I've been doing some searching on different sites for a 340 6pack setup. The new ones do not come with a Idle solenoid. The new dealers say it isn't required anymore, but they don't say why. My question is what exactly is different between the old set up and the new one as to why the new one doesn't need the solenoid? Different Idle curcuits? Better Quality Control standards? ...or ? Thanks, JOE