chemically speaking, considering the reaction, you have two things to consider: energy and time. basically heat relates to energy, and if you dont have enough energy, you will never make the cross over the activation energy barrier, or the inital energy hump required for the reaction to take place. From a molecular viewpoint, the water molecules have to gain enough energy, or speed/power, to run into the tea molecules and pull them off into the water. So in the most extreme circumstances of very low temperature, the activation energy will never be reached, and tea will never brew.
At room temperature, tea does brew, thus you know there is enough energy, but it is very far from the required activation energy. This is where time plays a larger role. Energy of a system is not completely uniform, some molecules gain more power when its more important with well timed bumps with other molecules. Although the NET or average energy is the same, some molecules are higher than others, which allows them to break the activation energy. thus, more time means a better chance that water molecules randomly gain the required energy to pull tea molecules and thus steep.
so instead of waiting, we can just increase the energy by using hot water and thus ensure that the net energy is already very near the activation energy, then time doesnt play a significant role, and thus the water molecules can easily bombard the tea molecules and steep quickly.
In other words, the way i see it, high energy or low energy, tea is gonna steep the same way eventually, and thus hot water or room temperature water will get you the same nutritional results, just hot water will get u there faster.