A "slabbed" coin is a coin that has been graded by a TPG, or "third-party grader" (preferably either PCGS, NGC, or ANACS) to show its condition. The grade there is MS-69, which is a tiny notch below perfect. For regular coins that were made to be used as daily money, an MS-69 designation can significantly increase the value of the coins. However, these are bullion coins that were never meant to be circulated, so they should be in near-top condition anyway. So most dealers don't give a crap about whether they are MS-69.
Here's a link to the "unslabbed" (or "raw") coins. They are several hundred dollars cheaper, although still more expensive than the Apmex coins:
http://goldlinecoins.stores.yahoo.net/bugoamea.html