Why this script doesn't work ?

The script:

tell application "Finder"
        activate
        repeat
                set w to display dialog "salary?" default answer "2000"
                set wSal to text returned of w
                display dialog wSal
                --processing of wSal
        end repeat
end tell

When running this script on my computer it's impossible to change the
value (2000) inside the display dialog window; why?

Thanks in advance

Pierre