How would you interpret this search volume discrepancy?

[krx]

I found a 4 word (20 letter) phrase that gets almost 500 on Wordtracker and over 850 on Keyword Discovery. But it gets no OVT and almost nothing on Google Adwords and nothing on Microsoft AdCenter. It gets about 10,000 hits on a google search (in quotes) and < 1000 on Yahoo. The word order is correct and the phrase makes sense as a search query. How would you interpret this?