What happens if the user goes to example.com, example.com/, example.com/index.html
Useful question. "example.com" without slash is not a problem, because the browser itself appends the slash.
"index.html" is two different issues, because it can come from two different places.
One: mod_dir will silently rewrite any directory in / to add the appropriate index file. This is its job. Usually this happens after mod_rewrite, but if you want to be safe, you can add a line saying {THE_REQUEST} index\.html to keep from going around in circles.
Two: users who really request "index.html". It goes without saying, ahem, that none of your own internal links use this form. The name of a directory ends in /. So that leaves the type-ins. They need to be forcibly redirected to directory-name alone.
Now, I have belatedly noticed two problems with the "pattern" side of your rule says. First, it says "/" rather than nothing. Does the slash work? On shared hosting it isn't supposed to. Second and more urgently, there are no anchors. That means the Rule will apply to
anything in any directory-- including non-page files.
You need an extra step that says, generically,
RewriteCond %{THE_REQUEST} index\.html$
RewriteRule (([^./]+/)*)index\.html http://www.example.com/$1 [R=301,L]
Since Redirects go before Rewrites within your mod_rewrite directives, that automatically takes care of the intentional index.html...
...leaving only the ickier, messier question of people who enter the site somewhere other than the front page.
