I think it's much better to do URL parsing in the script, just like some CMS do.
Badly written long long list of RewriteRules so common to "Short URL/SEO friendly URL" hype
is a goof way to waste server resource and complicate your life, IMHO.
Since you are using PHP anyway, why not to use it's facility?
It's much much easier to do it in PHP (for many people) and it doesn't tax the requests for non-php files.
This goes in myblog.com/.htaccess (or Virtual host section with <directory ... >)
RewriteRule !^index.php index.php [L]
And in the myblog.com/index.php, you check $_SERVER['REDIRECT_URL'] or
other env variables to get the URL, and parse it if needed.
You should be able to find lots of examples in OpenSource CMS/Blog code, too.