I think it's more a problem with famous quotes.
Try this Google search...
when in the course of human events [google.com]
Many books about the Declaration of Independence.... not many high ranking returns for the Declaration itself, and I don't think I would have found it in the top 10 had someone not quoted it in their page title.
I tried Advanced Searching "in the text of the page," which changed things slightly, but not much.
But, if I search for this obscure quote from the list of objections to King George further down in the Declaration...
He has made Judges dependent on his Will alone [google.com]
The lesser known quote returns many more copies of the Declaration, because no one has quoted it in a page title or heading.
The inherent difficulty with quotes occurs in fact when they're quoted (and used for other purposes). This is where I wish that Google had either a quote: operator or else an advanced search option to address this.