Save-as also provides the function of being able to save to different media/locations. Furthermore, it is easy. Power users already have their more powerful alternatives and non-power users are used to what they know.
How many times have you heard someone complain they failed to save their work? It just shouldn't happen - the computer knows exactly what was inputed - why should it ever lose track of it.
The "Save" function is a carry-over from the time when storage was expensive and slow, and humans had to make decisions about what was worth saving. Now, computers generate a lot more useless logfiles that are saved forever than a human can possibly generate using a word processor, and yet we are asked to make a decision about if we really meant to put out inputs into a computer.
That shouldn't happen any more, and with good software it doesn't.
In Google Docs - for example - there is no "Save" function - it happens everytime you press a button. There is no "Save As"; instead there is "Rename..", "Make a Copy.." and "Download As.." which perform the distinct functions rather than overloading "Save As.."
I have no idea what point you are attempting to make. Non-power users don't need full-blown version control, there are plenty of more straight-forward ways of making sure users don't lose their data than that. Save-as is not mutually exclusive with automated backup systems, or undo systems.
Furthermore, nobody is forbidding them from using the tools "power-users" use. The only difference between power users and regular users is what tools they choose to use.
I have no idea what point you are attempting to make.
Do you believe the solutions we have today are decent enough and cannot be improved further? I wish handling files was so simple that even those you call “non power-users” (i.e. pretty much everyone) could work with versioned files.
"I wish handling files was so simple that even those you call “non power-users” (i.e. pretty much everyone) could work with versioned files."
We have that already, it's called persistent undo and/or save as. Stunningly, a versioning system designed for the technologically illiterate doesn't measure up to one designed for coders.
Auto-save is a separate issue, but we have that as well...
If it ain't broke...