They do try search combinations with some words omitted, and right at the bottom of each query they tell you which part of your phrase they have excluded.
Yes, if I search for "Windows 7 NAT", dropping the NAT keyword returns more results. But none of them will give me the information I'm looking for.
This is especially true when what I'm searching for yields almost no results. That's how I typically know that what I'm searching for was probably bogus to begin with. But when the first page is full of a bunch of fuzzed-out results that are only tangentially related to what I searched for, I now have to skim through a page full of results to realize that Google just gave up and decided to omit several of my terms.
And they weren't at the bottom, they were actually the first result on the list.