Yes. That is absolutely what I am saying. It should be automatic. A simple "if, then" command:
IF it is between xx:xx PM and yy:yy AM
AND plugged in
THEN activate do not disturb
I shouldn't have to go into settings to change things every night. On the Blackberry this was all automatic.
So why not just set it for your "usual time" and on the rare occassion you are out and about turn DND off? I plan my life around the 80/20 rule. If 80% of the time I do X, then I set my settings for that so that only on the 20% of the time I am not doing X that I change my settings.
Edit: And yes, having a setting for charging would be nice. Frankly Apple just added DND with iOS 6 so prior to that we were all using the Sock/Cloth method mentioned previous! DND his a huge leap forward for us.