This is intended behavior, but you can change it if needed as documented in the article about editor configuration.
Most users do not know much about HTML and this is intended to help them do the right thing, the site heading or logo is usually h1 and the content instance heading is usually h2 so for most content edited within the editor headings should start at h3 because it doesn't make sense or good markup structure to use h1 below h2.
Hope that helps,
Joe