[Delmania]

A bit of history helps to understand why vi(m) operates in this fashion. Vi was first released in 1976 as the visual editor to the ex line editor. The networks were very fast in that time period, so it helped to "load up" on commands before you submitted them to gain as much productivity as you could:

"Joy explained that the terse, single character commands and the ability to type ahead of the display were a result of the slow 300 baud modem he used when developing the software and that he wanted to be productive when the screen was painting slower than he could think."

Taken from: https://en.wikipedia.org/wiki/Vi

An example to me, of how something pragmatic (wanted to avoid round trips) took on a life of its own.