I don't think any of these things have anything to do with "hanging out" and "class". When you get a book on your Kindle, you're not hanging out with anyone, you're just getting a book. Also, anecdotes and data notwithstanding, the times I've seen people "hanging out" with people they didn't arrive with at a grocery store in my life can probably be counted on one hand.

When your (cash-rich, time-poor) friends buy books on their Kindles instead of going to the library, it's most likely because they value the convenience of (a) not having to go to the library to get the book (b) not having to consider whether the book is stocked (c) not having to got to the library to return it (d) not having to keep track of when the book must be returned (e) not having to actually carry a physical book around -- more then they value their $10-15.