Have you read Dodie Smith's I Capture the Castle? Its narrator Cassandra talks about her dislike for what she calls "brick-wall happy endings--I mean, endings where you never think about the characters after the book is finished" (quoting from memory so probably inaccurate, sorry), very much what you're saying. I think she agrees with you and Jackmerlin that closure can end up making a book less interesting for the reader, depending.
For the record, I like happy endings myself, and tend to reassure myself in non-closed situations by thinking "Well, I'm sure Nicola and Esther made it up the next term, or Esther found someone else to be friends with," "Well, I'm sure Cassandra eventually ended up happily married to [redacted]" (in the book above) and so on. But having it not clearly stated by the author does strengthen the sensation of "these things happen because they would happen," not "because the author forced them to do so".
Not very coherent today, sorry...