Is it possible to change Versions' save frequency?
For some kind of work, one hour's worth of work is too much to lose!
I haven't been experimenting with this for long enough to be an expert yet, but I think you're confusing two semi-separate features: autosave and versions.
Autosave saves frequently -- in TextEdit, it seems to save after about 30 seconds of inactivity. But it doesn't save a new version, it just saves the current document state.
Every hour and/or every time you explicitly save a version (Command-S), it saves a restorable version -- one that you can revert to if you decide you've made a mistake in editing. Once saved, the "version" does not get updated; you can revert to it, or go into the Browse all Versions interface and copy content from it, but it's essentially frozen.
Autosave protects you against forgetting to save changes. Versions protects you against mistaken edits you wish you hadn't made. They operate on different time scales (and as far as I know, neither has customizable timing).
So, actually, the Versions part is Time Machine renamed, with a little addition: making it possible to force a separate Time Machine backup for a specific file. Autosave saves every 5 minutes, or during idle times while working on a document. See HT4753, as linked to by Graham.
Considering the misleading "Each time you open..." I think Apple refers to the first autosave action after opening a file. I tried this using Textedit and found that if you open a file, make some changes and then close (do not use the explicit "save a version" or cmd+s command) the file (or wait a bit) a separate version is being stored, instead of the default overwrite action autosave uses.
So it is a little more intelligent about saving a version "every time you open" a file. Making changes is necessary. Could have been pointed out in the KB article though.