OK but as I personally see no need for escape in my use of vim, I judge it to be equivalent for my purpose (returning to normal mode).

So how is it different?

^C interrupts the current operation, while ^[ actually finishes the input sequence. The only practical difference I can think of is that when you entered input mode with a prefixed number, ^C ignores it. So 2iabc^C only writes `abc', but 2iabc^[ writes `abcabc'.

Edit: apparently ^C also ignores abbreviations. :ab lhs rhs, then ilhs^[ writes rhs, but ilhs^C writes lhs.

Also, ^C doesn't trigger InsertLeave autocommands.