When the counters reach their maximum count, they're cleared back to zero and the PWM output is updated. In this example, the counters roll over after 10 counts. In the beginning, the rising edge counter is cleared and the output is driven high. Similarly, the falling edge counter drives the output low when it rolls over. That's no coincidence.
Binary counters are certainly the most common.
For example, suppose we're dealing with 8-bit bytes. These range from 0 to 255. If we were to put one of these counters into an infinite loop, it would start at 0, count up to 255, roll over to 0, count up to 255, etc. In the example psuedo code shown below, the binary counters are N-bits wide. Fortunately this technique scales up quite nicely for multiple pwm outputs.