Survey - Why employees quit

Interesting survey on why employees say they leave a job, as compared to what employers think is the reason. Inadequate compensation tops the list. (Employees 56%, Employers 46%). Second and third highest reasons - inadequate professional development opportunity and, insufficient recognition. More after the jump.
Biggest gap - 38% of employers say poor relations with managers, but only 22% of employees specify that reason. Similarly 28% of employers believe stress and unfair treatment are reasons for quitting, while only 22% of employees say thats a reason. This is interesting. The results differ dramatically from the surveys on reasons employees seek unionization. Wage/benefit issues are usually low on those surveys with treatment by supervisors normally stated as the number one reason for seeking a union.  Is the explanation rooted in the personality of employees seeking more as compared with the less adventuresome seeking to insulate the status quo from unwanted management intrusion?