Differences in the traditional way to handle each fruit. Apples dont like to give up their juice so you have to press them to be effecient though some people crush up crabs and make crabapple wine from them, thats because crabs have so much flavor and acid you can do that, but normal apples you got to crush and press. As for berries, who said you cant use 100% juice, if you can find a way to handle the acid levels nothing is stopping you from using 100% berry juice. It also depends on flavor intensity, 1 gal of apple juice in 5 gal of cider is lost, you wont ever taste it, but 100% elderberry juice is a bit much for most people. With berries they are usually frozen as they are picked until you get enough for a batch, then thawed and I think the best way is to them smush them up, not breaking up the seeds, adding pectinase and let it set overnight and you can either strain out the seeds and pulp being careful to not squeeze the bag to hard that lets more sediment out or you can ferment on the pulp depending on how long you want, like 3 days or longer than a week. You guys are searching for one way to process all fruit, there isnt one, you have to adapt to each fruit.
WVMJ