There are 4 formats available for the Title Module: H2 through H5.
Accessibility requires a logical heading structure, which means each page must have one level 1 heading (H1) and then follow a logical hierarchical structure from there. This means no skipping (e.g. using H3 when the are no H2 headings on the page).
The title of each page is automatically set has the top level heading (H1), which is why the first level format for the title module is level 2 (H2).
The Text Module also has heading levels that allow webmasters to properly build the heading structure of a page.