That's the idea, it's defiantly not a percentage based way of training. Every workout has it's own max which comes in waves. Some days you'll be "overtrained" and your max might drop 20kg. But if you keep at it gradually on those good days your max will beat your previous highest max. Doing it this way also lets your body get used to the feel of maximum weights all the time so you get used to the point just before technique breaks down.
And another poster asked about my training background, I've been training 2-3 years now. I started with SS (hence why i'm posting this here) and made excellent gains, i then went on to do some very successful 5x5 cycles. Afterwards I wanted to try shock my body into something different so I tried 5/3/1 which increased my overall cardiovascular fitness due to the high rep type body-building supplementary exercises. Percentage based programs have stopped working for me and i can see their inherit weaknesses so i looked elsewhere, the only two training methodologies i could find that would suit my needs is Broz Bulgarian style or Westside. To me the theories behind what Broz is saying makes a lot of sense and both methods have produced some amazing athletes so I'm sticking with his program for now (I train at home so Westside would be difficult). I've been on the program for a couple of months and it's true, your body will adapt, you will feel like shit a lot of times but you have to man up and do it, it's amazing what humans can accomplish when they put their minds to it. I'm up to 6 workouts a week (taking Sunday off), due to time constraints i only plan to do 1 workout every day and to make up for a lack of morning workout, I just increase the volume.