However for keyboard shortcuts said conventions are defined for crippled keyboards without dedicated navigation keys and the extension for PgUp/Down is simply inefficient when programming.
The cursor movement conventions have existed in macos since the classic mac days, when Apple was routinely shipping keyboards with "dedicated navigation keys":
Up / Down: move cursor one line up or down
Left / Right: move cursor one character left or right
Option+
Up / Down: Move cursor up or down a whole paragraph
Left / Right: move cursor left or right a whole word
Command+
Up / Down: Move cursor to the beginning of the document
Left / Right: Move cursor to the beginning or end of the document
Page Up / Page Down: Move the scrolled display area up or down a "page" without moving the cursor
Home / End: Move the scrolled display area to the beginning or end of the document
The latter two are nice to have because it means you can scroll up through a window to view something, and start typing to have your view snap back to your cursor position.
Additionally at least as far back as the Powerbook G3 "Wallstreet" in 1998, and including the iBook lines from the same time period, to the best of my knowledge every Apple portable since (as well as any wireless/compact keyboards with Fn keys) then has supported Fn + Left/Right for Home/End respectively and Fn + Up/Down for Page Up / Page Down respectively. They were even marked as such through the early non-unibody MBPs but continue to function that way today even without the markings. While these aren't dedicated keys, they're convenient enough in combination with the other modifiers that you'd be using to move the cursor that I don't personally consider it a significant difference.
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However for keyboard shortcuts said conventions are defined for crippled keyboards without dedicated navigation keys and the extension for PgUp/Down is simply inefficient when programming.