It is not so much a power trippish issue. It is the fact that whilst part of our job is to make actors comfortable, there are so many more issues deserving of our time. Small theatres, the on stage drinks are usually made by the SM or ASM.
Now I am unsure about the rest of the people here, but I usually make the quantity I will need on the night, whilst doing my pre-show work (I rarely have access to a fridge for storage, and I am against the serving of stale water). Frankly, tea is the most time efficient, and the easiest method.
If actors do not like tea, then I am open to alternatives, however if it is anything more complex than placing an item into water, or if it involves making large quantites (ie due to the strength of one ingredient) then the logistics will probably end up being the actors responsibility, because I believe that my time can be better spent else where in most shows - like making sure everything is ready to go.
Re "the joy of making something 'work' when it was thought not possible" - true, it is enjoyable, but tea WORKS. It is not dangerous, it does not have any ill effects upon the actors, all they have to do is put up with the taste.