.htaccess RewriteCond

[zylstra]

I have the following in my htaccess file:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !/(admincp|modcp|clientscript|cpstyles|images)/
RewriteRule ^(.+)$ vbseo.php [L,QSA]

Why is the third line needed if I have already determined that the directory does not exist with line 2? Doesn't line two state, "if the request is not a directory"?