Maybe you should reverse the question. Why has software development always been about productivity? What is it that makes people really happy, being productive or having a rich social life? (Depending on your needs 'rich' may be just that one special person, but still.)
It's funny you use 'a simple web-based address book' as an example, since an address book is kind of a useless tool if it didn't have a purpose: social contacts. In a world where 'everyone' is 'connected' it's only natural to start looking beyond that and look for way of directly connecting the addresses to the actual social contact.
Games aside, we are only now starting to look beyond the mere useful and productive when it comes to software, it's a new and exciting field, with lots yet to be discovered. And as an added bonus it's actually already proving to be useful too.
Maybe the 'social' is being overemphasized right now, but that's only natural. For a lot of software uses there is no real hard separation between the useful and the social, it just wasn't possible to make that direct connection until now.
No offence, but I kind of agree with 'that guy', if the software has a natural social aspect, it isn't really complete without it. It's like a webshop that doesn't allow you to order stuff, just make a printout and take it to the store.