This article explains if users write their own driver if it will need a calibration routine

You might be okay if your touch zones are large enough and spaced far enough apart.  However, the issue of touch orientation is a much larger issue than that of actual calibration over the screen's area.

 Sometimes touch screens are installed "flipped", as in rotated 180 degrees from the expected alignment.  This is usually due to cable length and controller placement inside the monitor.  Also, some touchscreens are designed with the X and Y axes physically swapped; this is due to screen design needs.  In other words, you cannot be sure the touch 0,0 origin will be where you expect it, and for that reason a calibration procedure is sound driver design practice.