Schnack seems to provide a simple solution to the "let us put some comments on the site" in a very simple and pleasantly small package. (Like seriously small, we're jealous of those numbers :))

Talk on the other hand provides a full admin panel for moderators, a robust plugin system for configuring every part of the experience.

Admittedly, not every small blog is going to need all of our features. If you want comments to work on your small site, Schnack seems to suit that role fine. Talk on the other hand is currently supporting millions of users and tens of millions of comments. It's a matter of scale really, both are great solutions that take the data out of a marketers hands.