Differences between Google Voice and Google Talk?

Question

This webpage reads:

Google Voice can interface with ordinary telephones while Google Talk cannot

Then

1. Why does Google Voice needs Google Talk to make an outgoing call?
2. Why using Google Talk itself can also make a outgoing call?
3. What differences and relations are between these two, in terms of both their technology and user usage?

Answer 1

Originally, Google Talk (and the Gmail and Orkut integration) was an entirely separate product from Google Voice.

Next, Google Voice was integrated into the Gmail Google Talk implementation and then, recently, into Google Hangouts (Google+) as well.

Google Talk itself, as a standalone product, has been more or less killed.

Google's goal right now is to roll out Google Voice internationally and meanwhile slowly integrate the two of them together. Seeing them as entirely distinct products might not be entirely valid anymore.