If you check the URL for Google Hangouts you'll notice it's pointing to the old identifier for Google Talk (com.google.android.talk):

https://play.google.com/store/apps/details?id=com.google.and...

You'll notice this same link is used in multiple locations promoting Google Hangouts:

http://www.google.com/+/learnmore/hangouts/

It looks like they temporarily pulled the Google Talk app to transition everyone to Google Hangouts without needing users' intervention (except maybe upgrading the app).

Edit: Just installed Hangouts app, it replaces Talk. Also it asked to confirm my phone number, hinting at future SMS support?