Hopefully it is not necessary to precede every statement with a legal disclaimer that I am not representing the universe.
Giving up your last VP is suicide, there is no grey area. It is the end of the game for you. Giving up gems does not end anyone's game. It might end someone's game in a turn, but even then it requires time for the enemy to receive and make use of them. At any rate, trying to analogize the two requires you taking a very extreme case of gem gifting to even come close to the suicidal impact of giving up the last VP.
Taking that extreme case aside, giving gems has much more nuanced and strategic purposes then killing yourself. It seems pretty close to fact. I went to law school and am comfortable with terms like "reasonable efforts" or "prudent standards", in other words - using your judgment.
I would not waste 3-4 hours to play a board game where one player was just going to quit, by granting his points to another as the game neared its conclusion. Why should I waste 12 months and 100s of hours to do so in Dominions?