When I first started writing HTML stuff back in 1997 on my first GeoCities site, it was plain old HTML.
Ex:
<![CDATA[
<br>
<hr>
]]>
Then XHTML came around and now things all required closing tags. So, I got used to adding closing tags to everything.
<![CDATA[
<br />
<hr />
]]>
Now, we're past XHTML and now the closing tags are no longer needed again and are optional. I still find myself using them because it's become baked into my brain at this point.
I guess it's not a big deal because either work these days but if you look at the source of this page, there's a mix of "br"s with closing tags and not (fixed in next release).
It's one of those things where it's not exactly wrong but it's not exactly correct for HTML5 either. I guess for now, I'll stay with the XHTML way.
Though, I can't say I miss having this huge thing at the top of the page:
<![CDATA[
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-US">
]]>
"Forces act when not restrained" - Puckdropper