Training program for duathlon

Hi all,

I just found three training programs for duathlon:

http://www.bhf.org.uk/get-involved/events/training-zone/triathlon-and-duathlon-trainin/triathlon-and-duathlon-trainin.aspx

These training programs do not include any strength training, what do you think? What will be the impact of not doing any weight lifting?

Thanks,
Jamal