I don't understand how a fruit tree, say an apple might end up getting
pollinated by as many different types of apple trees in the area close enough
for bee travel or wind and yet all the apples will be the same, even with all
the possible different types of pollen that could have been involved in
fertilization.

OK, suppose you have a 'Granny Smith' apple tree, and your next-door neighbors
have 'Empire,' 'McIntosh,' and 'Cortland.' When the flowers on your tree are
pollinated, your tree will produce only 'Granny Smith' apples. The genes in the
fruit producing part of the tree have not changed. Only the seeds in the apples
are affected. If you planted the seeds of your open-pollinated 'Granny Smith'
apples, you would get a mishmash of all different varieties. Even if you could
fertilize a 'Granny Smith' flower with its own pollen (most apples are
self-sterile), the offspring would not be 'Granny Smith.' They might be similar
or different, but would not be the same cultivar, which can only be reproduced
vegetatively.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)