I think there are both - the friendships and what I'd call the 'one night stand'. To each their own - some people prefer the friendships, others, like you it seems, prefer the 'one night stand'.
There have been quite a few threads about this topic
This thread had a poll about it too, and you'll see that about one third of the responders prefer the friendship route, one third prefer the one night stand, and about one third go both ways (no pun intended).
This thread asks almost the same question you did.
Read through those threads and you'll see that you are not alone in your thoughts, nor is your wife. Your 'problem' is that the two of you disagree, so some compromise will have to be reached.
We have tendencies towards both ends of this spectrum. We truly enjoy the 'one night stand' for sex only. And we've met some wonderful couples that we consider friends.
Sarah