Generally speaking doing all your sets in the 20+ rep range for the purpose of building muscle is a horrible idea. Will it build muscles? possibly, But the problem with high reps is you can not take your muscle to failure.
If you use heavy weights in 8-15 rep range your muscle can go right to failure and 1 working set per exercise will yield great results.
What the misconception is while doing higher reps (20+) is that you are taking your muscles to failure, while it may be true that you can not perform another rep, but this does not mean that the muscle involved has gone to failure.
During high rep sets lactic acid is the culprit that enables you to move on beyond a certain barrier and it is more likely that your muscle has not reached failure when lactic acid kicks in, furthermore during a high rep set your tendons, ligaments and joints will get sore quicker then the muscle will, so failling in a set of 20-30 reps does not mean you put a lot of stress on the muscle for growth.