V-Speed accuracy on complex models.

I have noticed that no matter what aircraft model used (Wilco/Feelthere, Level-D, PMDG, CS) the calculated speeds for V1 and VR are within 1 or 2 knots, and in many cases the same speed. When I watch though real world cockpit takeoff videos, it appears the gap between V1 and VR is greater, more like 5-10kts. So my question is do pilots routinely override the calculated speeds, or is there a problem within FSX on how these speeds are calculated?