I guess there are two things to take away: (1) in most games (i.e. those without a timekeeper) make sure time expires before the try or conversion - little good will come for a referee who restarts because he still has 10 seconds left; and (2) you can't have a lineout following a penalty awarded in stoppage time - so again it might be appropriate to ensure that time has elapsed.
I find this unduly cyncial, and rather unfair on the team that are 1 point behind and are entitled to have the game restart..
I mean if you follow your logic then if you have any kind of stoppage in the last minute or two you'd blow for full time to make things easier for yourself.
Doesn't fairness and equity dictate that if there is time left on your watch you keep playing.