After looking through the book "Feedback control of Dynamic Systems", I should say the clockwise encirclements are as much mentioned as the counter clockwise encirclements. However, the importance of both differs whether the open loop transfer function has unstable poles. So as you might know, N the number of clockwise encirclements in the nyquist plot, equals Z the number of unstable poles in the closed loop transfer function minus P the number of open loop unstable poles. P is in these examples assumed to be known. it is desired to get Z = 0. Therefore, if the open loop has RHP poles (P>0), The nyquist plot should have P counter clockwise encirclements. However, if the open loop has no poles in RHP, there should be no encirclements of the point (-1,0) in the nyquist plot. Every encirclement (which can be assumed to be clockwise) will show that the closed loop TF is unstable. If P > 0 and you count clockwise encirclements, the closed loop has more poles in RHP than the open loop has. So in short, counting counter clockwise encirclements to achieve stability, if there is a clockwise encirclement (you dont have to count), the system is unstable anyway.
I hope this helped