I'm not sure if there was any change to the rates, but it could be a biome thing. Example, swamps were typically a better place to find apples since the oaks there, although small, would have a higher proportion of leaves on them.
That being said, large oak trees grow naturally in plains now which I believe is somewhat recent, and I noticed they grow more often in forests during natural generation with some forest biomes just being full of the large oak trees. Honestly, the forests with mostly large oak trees look like a whole different biome on its own.
Perhaps apples seem to be more common due to the increase of large oak trees since they do have more leaves.