h1b petitions reconsidered after other h1b rejections?

I have a doubt. Consider, there is a lottery, and 65000+20000 petitions are selected. Later, some of these petitions would be rejected due to some or other reason. Will they consider more people from the original list, or are those slots gone.

What I want to know is - are 65000 visas granted, or 65000 visa petitions considered.

Thanks!

USCIS has “wait-listed” some H-1B petitions, meaning they may possibly replace petitions chosen to receive an FY-2009 cap number, but that subsequently are denied, withdrawn, or otherwise found ineligible.  USCIS will retain these petitions until a decision is made whether they will replace a previously selected petition.  USCIS will send a letter to the wait list petitioners to inform them of their status