Have a look at the Data Dump schema. Jeff's comment makes more sense in that context.
Also, your terminology between what's meant by revision and record is confused.
The Posts table stores only the current state of each post (i.e., the latest revision), and the PostHistory table stores information about how a post has evolved (i.e., each record contains part or all of a revision).
Now, revisions. They are created under several circumstances, which apply to all types of posts:
- You create a post (ask a question, answer a question, create a tag wiki)
- You edit a post and more than 5 minutes has elapsed since you posted or edited the post *
- You edit a post where you are not the most recent editor (or owner) of the post
- You rollback a post to a previous revision (with or without edits)
What gets put in PostHistory for each revision depends on what was changed. For answers and tag wikis, those only have post bodies, so they would get 1 record each. A question, however, is broken down into title, tags, and body, so for each one of those components that was changed, a new record is put in PostHistory (with a suitable revision identifier to group them together).
So, yes, 3 records are created in PostHistory (and 1 in Posts) when you ask a question, but it all constitutes a single revision.
* There is a bug with the in-page retagging tool that always creates a new revision, regardless of the amount of time elapsed since the last edit.