Yes and no. I think it's a matter of interpretation. A witness who doesn't post frequently enough is, technically, useless for the network integrity and to assist normal nodes to have their transactions validated as fast as possible. So, that means this lazy witness is potentially a bad witness and should be exclude at term. A temporary lack of posting could be obviously tolerated when there are technical reasons but it should be limited in time.
So, in my opinion, a witness has a mandatory behavior to be selected/elected as a good witness.
A witness is incentivized to post frequently enough. This is not the same as having mandatory behavior.
Technically, if 7 witnesses stop posting, network halts. Due to a law enforcement, they could have to do it, who knows... Witnesses have to be very distributed over the world.
I think almost all users/all potential users don't care about witnesses selection, like me. They will accept whatever byteball foundation say. Or better said, what byteball.org/bb says regarding to witnesses list choices.