If section numbers are turned off, then start with first-level headings.
If section numbers are left on, then start with second-level headings. The reason for this is that the numbers in front of first-level headings look ugly and distract from the content of the page.
Why not hack on the style instead? --AdamChlipala
Because the size of the normal unnumbered headings look about right. Perhaps we should just turn section numbering off globally. I could do that easily. --MichaelOlson