Whew, I am not getting it. The overture keyword suggest tool gives me 193,000 searches per month for a particular keyword. The first site, however, claims that they are getting 19,000 visitors per month. Their claims could be bogus, but the second site has public stats available and it clearly says something like 12,000 visitors per month.
When you consider that Google is the biggest things out there, then it seems highly unlikely that the number one site is only clicked for 10% of the results that the overture suggest tool shows me.
What does the overture tool actually show me and how is it kind of realistic to calculate the number of visitors that I could expect when I would have number 1 spot on Google (yes, I know that it is a big if :p).
thousands of webmasters checking their serps- sometimes hundreds of thousands.
The other factor is that the searches are aggregated between plural and singular.
The other factor could be bots triggering searches for numerous reasons.
Another reason, prolly not in your case, but in some cases it's because some webmasters are inventing phrases and clickbotting the numbers up so that their competition will optimize for the bogus terms while she optimizes for the correct term.