If you want to get to a brand's like-count, you'll need to feed the Graph API with either the Facebook Username of the account (e.g. "nike", not "http://www.nike.com "), or with the Facebook ID# of the brand (e.g. "15087023444").
For example, the script gets a count of 1,257,333 for www.apple.com:
https://graph.facebook.com/?ids=http://www.apple.com
Which from here we can see is the sum of the 3 values:
http://api.facebook.com/restserver.php?method=links.getStats...
And by entering www.apple.com as the URL here we can confirm is exactly the figure the Like button shows:
http://developers.facebook.com/docs/reference/plugins/like/
So whilst maybe not 100% accurate in some regards, it is certainly what many people would refer to as the 'like' count (and they'd be confused if you gave a lower number which isn't what the like button on the page showed). This tool is aimed more at URLs than brands.