On Windows python wakes up too early

Question

from time import clock, sleep

for i in range(100):
    t1 = clock()
    sleep(0.123)
    t2 = clock()
    print(t2-t1)

Why are most of the timings below 0.123?

On unix (using time.time() instead of time.clock() as suggested in the manuals), all times are above 0.123 just as expected.