>>Because VFP is not really ANSI complaint and has its own implementation of SQL language. That's why VFP has different syntax. I don't know if internally in VFP that expression is calculated more than needed but in SQL Server in doesn't calculate in both places.
>
>How did you verify that in SQL Server having the same expression ( (COUNT(....))>5) ) is not being calculated in both places?

Try running with showing execution plan. You can also use

SET SHOWPLAN option

See

http://blogs.lessthandot.com/index.php/DataMgmt/DBAdmin/MSSQLServerAdmin/getting-started-with-execution-plans