[rtpg]

Hmmm... yeah that's a good point. Though I would contend that the fact that languages do not do this is indicative of... something.

[tsimionescu]

I would guess that the main reason is that the on-stack way only works for local variables. If you want to pass anything else by reference, you need to use some kind of address to it, since it's not in the caller's stack anyway.