AF the thing you said about the barbecue is the sort of thing I can categorically say my DH would never do. If there was a planned commitment then he would honour it, and getting stuck in the pub would not happen in that scenario. He isn't thoughtless or deliberately selfish in that way iyswim. If he knew I needed him home for a specific reason he would be there - no question.
mylunch there is no need to be sad on my account. There are plenty of women on MN to feel sad for and I am not one of them. I am quite content to be in a happy if slightly imperfect marriage to a lovely, if slightly imperfect man. I don't think that makes me an object of pity - I think it makes me a realist. And being a realist cannot be overrated IMHO.
If his occasional embarrassing behaviour ever reaches a stage where it is a serious threat to our marriage then rest assured he will be the first to know about it. DH knows how I feel about this and he knows that if he started off with nine lives he is now down to about 5. 
But in the meantime I'm not really interested in whether it is 'normal' for anyone else's husband, or whether it would be tolerated by you mylunch , or AF or anyone else . I'm only interested in what works for me. The conditions and ground rules of other people's marriages do not interest me, and I don't judge the worth of my marriage based on anyone else's expectations but my own.
Good marriages are based on give and take - at least they should be, and the day I feel that he is doing all the taking and not enough giving I will deal with it. But all things considered I am a very, very long way off that and I have very little to complain about.
I think a marriage is in serious trouble when the level of contempt you feel for your partner is in danger of outweighing the respect and the fondness, and whilst I have undoubtedly felt contempt towards him on the odd occasion, it has never come close to the respect and the fondness I feel for all the things he continues to do right.