You could replicate this by starting a selection and manually moving to the end (either by a combination of commands), but it looses its coherency as a single expression to be executed.
In the words of someone smarter than me, you have a conversation with vim - "delete three words", whereas you micromanage another editor - "start selection, move one word, move one word, move one word, delete".
I understand why in some cases the kind of low level power you get with editors like vi and emacs etc is of an advantage, and I use vi regularly myself for basic editing on remote shells, but I am more of a visual person and I much prefer the usability over power approach.
Every movement is composable with every action. There's a lot of movements, and a lot of actions. Delete three lines is the simplest possible command, but it's hardly the only one.
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