Using a "key combination", i.e. a simply qualifier key like CTRL to start an action and have it automatically fall back into insert mode when that action is over, to me is far LESS restrictive than the current way command vs. insert mode works.
I lie in bed at night *dreaming* that someday this will make it into vim as standard...
...well, not quite, but it would IMHO make such a huge positive differences to the lives of all who ever have to do a small bit of admin or use a unix machine for a little while a whole lot easier....
(nb: the *only* reason I learned VI was as cited above by someone else: you can guarantee (almost!) access to it on *every* unix machine you ever need to use. Since many of us only use unix machines intermittently - e.g. just to reset a crashed server, or to alter a MySQL DB on a webhost, or to run some specialized unix-only network-diagnostic tool etc - it's very useful to have some editor that:
- you only need to remember 4 commands to be able to use completely
- is always installed everywhere
FYI, the only 4 I knew for the first 2 years (I used others, but not frequently enough to memorize them!): escape and insert to change mode, ":w" to save and ":q" to quit.)
FWIW, there is at least one *much* better text editor for *nix which is about the same sort of size as VI (i.e. counted in 10's of kb, not megabytes like VIM) and which any idiot can use.
Sadly, it is not widely installed, and I don't even know it's name! I found it on a "linux one-floppy router OS" that you can plug into any PC, boot, and have a working router + internet dialup + DHCP + DNS. (you have to run a program that generates the floppy for your particular hardware + ISP password etc). This editor has:
- menus using F keys, none of that Emacs sh**
- normal key bindings, including things like CTRL-Q for quit, CTRL-S for save, etc
- none of the confusion of multi-mode!
Perhaps someone here knows what it is?

But...the big thing about VI is that it's installed everywhere, and VIM almost everywhere, and until something else is installed as widely as is as simple, VI(m) will always be with us...