With the K series yes it seems to be the case just due to the ivtec design but again it can be tuned out so the power is more linear(not to everyones liking when vtec cross over is flat)
As for your B series if the car was bog standard you probably wouldn't notice any dip prior to vtec its when you add breathing mods and the velocity of air entering and leaving your engine increases that the engine will want to switch to high cam earlier in order to take advantage of this increased air flow, where as if you were to continue a couple of hundred more rpm the profile of your low cam(out of vtec) could begin to restrict the engine resulting in torque output flatening out or dropping off hence its often the case when tuning these that we can lower the vtec point from its set point of stock ecu to take advantage of the increased air velocity and pick up some midrange power however different cams, exhausts, intakes etc all effect how your engine breaths so we can't assume the optimum vtec cross over point will always be lower in some cases it ends up been higher than the factory set point.