It looks like Microsoft Search Server Express don’t search in the whole document collection when it is many results. For example for the query enron almost all the other engines have the Enron scandal document on it’s first page. But not Microsoft Search Server.
Looking at the result type filter, selecting something other then Word as result type isn’t even possible.
But searching for enron scandal directly shows results from both webpages, Word files, text and PowerPoint.
Don’t know if this is a bug or by design, but I can imagine that failing to return all documents for common words will cause problem for people with large document collection.