They very much are. One of my boys was killed because I didn't realise breeding season was starting and seperate them in time. There was zero warning signs, I remember they were fine that morning and then he was scalped and had fly strike by the evening :(
A stupid mistake I won't be making again.
Practically every single animals eats and drinks, most socialise too. Every single bird species preens and I am pretty sure chickens and quail aren't the only birds who dust bath.
You can't compare a chicken to a parrot (believe me I've tried :p), so you shouldn't really compare chickens to...
They're quite different to coturnix, because they're not good for eggs and I don't think I've heard of people eating them. They're more ornamental I guess you could say.