Will you are probably technically correct, it would be helpful if you could explain what they are instead. Because they're a bit more than just applied physics - the choice in jumping mechanics has a fundamental influence on gameplay, so there is at least some kind of relation to game mechanics.
You can look at it like this: mechanics are abstract, while gameplay is concrete.
The gameplay is what the player can actually do at any given point in the course of the game: move a piece, make Mario jump, shoot a gun.
Rules define both the valid inputs and the reaction of the game to player input: you can't walk through walls, monsters drop loot, XP lets you level up.
Mechanics are the higher-level constructs resulting from the feedback loops created by the game's rules, in reaction to choices that the player makes.
The example of Asteroids:
The gameplay is moving a spaceship and shooting asteroids.
The game rules state that you progress to the next level by clearing all of the asteroids from the screen. When you shoot a larger asteroid, it breaks into several smaller pieces. When you shoot the smallest asteroids, they disappear. Colliding with an asteroid means you lose a ship, and losing all of your ships means you lose the game.
The mechanics that result from this are evading the asteroids on the screen, judging the risk of shooting each particular asteroid, choosing the right place to be and the right time to shoot, allowing you to stay alive to eliminate them all.
Yes, it is more like these are examples of the building blocks that you build game mechanics around.
It is interesting that the author of the page calls them "examples for game mechanics" not examples of game mechanics, so he may be in agreement with you.
