Allthethings, I, personally, do find it immature to get so drunk that you have to stay over night at someone else's place. That's just my personal opinion. (and that's the way I read the letter. it didn't sound as if it was pre-planned)
My DH and I enjoy good wine and beer every now and then. However, if we were to go overboard and get drunk, we would grab a cab home. Staying at someone else's home makes me think of my falling-down-can't even mouth a syllable-drunk cousin. She's almost 40 and parties every weekend like a college student. She is immature. She never got past that phase in her life. Instead of a phase, it's her way of life.
Now, my cousin does this every weekend so she is not the norm but I can see why the LW would be annoyed at his wife. Drinking and paryting responsibly (even if it's only 5 times a year) is making sure you get home at the end of the evening.
Again, this is just my personal opinion and luckily, my DH and I are on the same page.