I would definitely say they are re-dosing after every change. On my high light setups I change 30-50% of water on a weekly basis. I use a python system. Since I have no chlorine or chloramine in my water (as my local water report tells me) I just fill the aquarium up via the python system and then dose the entire tank. I add in my dechlorinate (I use stress coat, used it on my reefs, and now planted tanks), stress zyme, equilibrium (Water lower than 1 degree GH), sodium bicarbonate (to bring up my KH) and then I re-dose my ferts. KNO3, and plantex on one day, and then phosphates on the next. I always just treat the whole tank. I add plantex+KNO3 and phosphate in small amounts and stagger the days I add them into the tank. Plantex and KNO3 one day, phosphate the next.
I assume those that change water daily just have a daily dosing schedule like mine and dose after their mini-change.
On another note, if I had to change water via a 5gal bucket system I would go crazy. This might just be due to the fact I have 6 aquariums. A Python system has been my best investment yet, even if it does waste quite a bit of water. I could just disconnect like some and drain outside, but that really isn't feasible in my living situation.