In previous versions of Indesign (I have just now tested in CS4) you could press shift-enter in the tabs palette and focus would remain on the tab setting. This would allow you to easily enter a precise value and move the tab stop. Pressing Ctrl-Shift-Enter would do the same but add a new tab stop. This meant you could easily add tabs at precise stops right from the keyboard without having to double click in the box every time. This would also make the behaviour consistent with the other palettes where shift-enter applies the value but keeps focus.