You know, I rechecked my sources and I stand corrected.
<hr> tag itself was not deprecated (there was discussion for it to be, once upon a time, and HTML5 ended up re-purposing it and gave it a slightly different purpose), but the inline styling like
noshade etc is no longer acceptable and therefore, would throw up the Validation errors.
<hr> now has functional meaning - it can indicate a pause in the flow of a document, for example like you said, but as such, probably should not be used as an underlining element.
As such, I still maintain that for true underlining rather than the literal breaking of a post/series of thoughts into segments, styling with CSS using either the underline ability or border ability is still probably best.
And yes, what you demonstrated would be a good way (aside from using the
<hr>) to automatically add a visual line spacer after the header.
I guess what it boils down to is what purpose is the line being used for, right? To underline, to separate content, or what?
Thanks for asking questions; helped me to clear some things, too, and sorry for the confusion. :)