I think the apple problem may be 'bitter pit' caused I think by a calcium deficiency
We have fruit trees here and I have always given them a handful of a balanced fertiliser in the spring.....like the rest of the garden.....
and don't seem to have the problem

I have had Bitter pit problems with Bramley and Ashmeads in the past. Chemix used to do packets of Calcium carbonate (might still do). I made deep holes with a big wrecking bar around the trees, where the feed roots are and put the powder down the holes. This seems to have worked. Putting a general fertiliser on may work if the trees are the only plants in the area, ours are surrounded by herbaceous stuff which, having shallower roots, pinch and food going long before the tree can grab it.
Bitter pit is also a seasonal thing, some years you get it, others not.
As for Pears going 'sleepy' (the term for them rotting from the inside) this again is a seasonal problem.