I similarly noticed that one of my three computers running Ubuntu 14.04 did not have ntp installed after selecting "use network time". I noticed this when one computer did not update the time for DST. Looking into it further, I realized it did not have ntp installed. Manually installing ntp solved the problem but I never manually installed this on either of the other computers so I am not sure why I had to for this one.
I similarly noticed that one of my three computers running Ubuntu 14.04 did not have ntp installed after selecting "use network time". I noticed this when one computer did not update the time for DST. Looking into it further, I realized it did not have ntp installed. Manually installing ntp solved the problem but I never manually installed this on either of the other computers so I am not sure why I had to for this one.