I know this is an old thread, but there is a lot of misinformation here . . .
The endpoint fellow has it right.
It's not called 3x3 because of any rep scheme. It's because you do the 3 lifts 3 times per week.
It's setxrep scheme is 6x6 bench, 5x5 squat and 5x5 deadlift. It's very brutally high volume, especially the beginning. Your weights go up by percentage constantly. Then, at week 5, you suddenly drop the volume to 5x4 bench, 3x3 squat and 3x3 deadlift. But for one lift each day (like bench mon, squat wed, etc) you drop the reduced volume sets even and do a 1RM up to 95% max. So weeks 1-4 are super high volume, and weeks 5-8 are maintenance volume training and max effort work. Don't forget that all your percentages are based on your new targets, not your currents. Your basically programmed into your new targets over 2 months.
It's really pretty basic. Some people like variety, but I'm in the gym to work, so I don't care. You will lose balance and muscle symmetry outside of the big lifts, but I care more about powerlifting now. I have found joint pain and cortisol to be big problems with these routine, versus westside which is a lot more laid back than these crazy eastern block programs. But I can reliably gain 40 pounds bench and 90 pounds sq/dl. I imagine it's best for beginners like me, who need more time with the basic lifts. It's also very good for strength sports like football. The problem with westside for beginners is not knowing the big lifts enough to know your weaknesses. A workout team or a great coach can help you, but I am alone. So for relative beginners (like 300-500 bench and 400-700 sq/dl) working alone, punching the clock with 3x3 is very reliable.
I added 200 pounds to my bench in 1 year keeping it simple like this. I recommend it highly to other newbs like myself. In fact a started another cycle myself recently to hit new prs (355b, 495sq/dl) jun 1
In between these I do wsb stuff after a little time off to recuperate.