about mod_rewrite rule: breaking 404 page access?

Hello,
I have found a disturbing problem with the default rule shipped in .htaccess located at the root of the Drupal script (which is my webspace root as well).

Here is the rule:

  # Rewrite current-style URLs of the form 'index.php?q=x'.
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

Now, any 404 in my site triggers the drupal index.php script.
I've changed it so that only urls beginning with /cms/ do get redirected, so this may help people too.

RewriteRule ^cms/(.*)$ index.php?q=$1 [L,QSA]

Does it possibly break things by doing this? That is to say, does any script or module require this rule to be left intact?