The count of results at Google can be very misleading – what logically should go down may go up. This can be the case between a search phrase with quotation marks and without. We expect more results if just looking for keywords anywhere, and less if looking for an exact phrase. This posting from Barry Schwartz for Search Engine Roundtable – Google’s Database Tiers – Searching Deeper – explains why the reverse can happen.
The answer is because Google will often search deeper into their index to find more relevant matches when you use quotation marks in your search. When you do not use quotation marks, Google doesn’t always search into deeper index tiers.