Ok, repeat after me... "The search numbers in the Google Keyword Tool do not show how many people actually search for that term in Google".
The numbers you are seeing are the TOTAL number of times that term was searched for AND had matching AdSense ads shown on across all of Google's partner sites. This does not include AdSense publisher sites, these are big sites with direct deals with Google like Mahalo.
This means that when a site like Mahalo has someone land on a page, they can select related keywords for it, Google shows AdSense ads specifically for those keywords and then logs it in their system as a "search".
Google has this sort of setup on many sites.
So why does Google show you this number in it's Keyword Tool? Because the purpose of that tool is to show you the potential number of times your AdWords ad could be shown for that keyword. That tool is for AdSense advertisers, not for SEO research.
So for a given keyword that has 40,000 exact monthly searches, you can't tell if 39,999 come from Google's partner sites and 1 comes from their search engine or if it's the other way around.
The only tool that Google has which will give you the numbers you're looking for is the Google Search-based Keyword Tool. Only downside is that it's database of keywords is much, much smaller than the AdSense Keyword Tool.