I don't think this is a tech industry specific thing. In a previous career in sales, all the conferences and events ended each night with a boozefest. The most common way to celebrate a sale was... to go out drinking.

Friends that are doctors or lawyers talk about conferences, which as I'm led to believe, are some possibly interesting talks during the day, and then a party/drink-up at night!

(I didn't drink during the sales phase of my life, and generally found there were other people drinking soda or able to handle their liquor and hold a real conversation at most events.)