Probably the fungal disease called scab causing the brownish/black spots and some yellowing/dropping of the most damaged leaves.
Spores are dispersed on the wind and land on the leaves. When the leaf surface is wet for several hours (including water droplets which remain for a few hours after rain stops), the spore can germinate and infect the leaf or the fruit.
Some years and some varieties suffer worse than others. There is no cure once infected, but the problem may not occur next year depending on the weather.
Some varieties have resistance to scab; especially the really rare varieties. The common varieties tend to be very prone to scab.
The leaves looking like they've been attacked is nothing to worry about, unless your tree is a dwarf and therefore unable to care for itself, Big trees don't need help. In fact, birds are often attracted to plants with tatty leaves in the hope that they can find an easy meal (a caterpillar).
Lack of fruit could be cold weather affecting bees (therefore no pollination). Sometimes frost can damage the flowers, as can other unusual weather conditions.
Some trees simply crop every second year - and it tends to be more noticable the older the tree gets.
In summary: if you're organic, put it down to a bad year, do nothing and see what happens next year.
Growing more than one variety can help because when one variety has a bad year, another may do well.