Options +FollowSymLinks or Options +SymLinkIfOwnerMatch is required in order to use mod_rewrite. The domain names should not be end-anchored in order to prevent rule failure in case a port number is appended, e.g. "widgets.com:80/index.html".
This is a relatively simple rewrite, so if it does not work, then it's likely that mod_rewrite is not enabled on your server -- Check your server error log to see what it says.
Because the period has special meaning to the regular-expressions pattern-matching language used in mod_rewrite. Without a preceding the slash, a period in a pattern means "match any character." Any character that has special meaning in regular expressions must be escaped if used inside a pattern.
In this case, it is used to specify that you want a literal period to match, and not just any character.
More info is available in the regular-expressions tutorial cited in our charter.