I completely agree with Bill F.
If you say or post you will be coming to one of these then it is normal that you are expected to attend.
If something comes up and you can't attend then post the night before the meet and if it is last minute give someone organizing the event a phone call.
Of course the organizer of these events should provide a contact number to each person attending with a PM so this is possible.

I am referring to the smaller local meets.
It is not expected with a meet the size of Woodward or the Dragon.