Hypertrophy can be achieved in many different ways. And after someone has trained for a lengthy period of time the only way to continue to move forward is to utilize various modalities.
For example, have you noticed that Power lifters while not training in traditional 8 to 12 hypertrophy rep range still gain considerable size? Also, we can see hypertrophy on long distance bicyclist. While their upper bodies are puny their thighs are massive. And that sort of training can certainly be considered very high rep!
My point is simple, there is no magic set/rep pattern that you must execute in order to achieve hypertrophy. Certainly if a beginner does four sets of 8 to 12 reps he or she will achieve a good amount of hypertrophy. But what happens after a period of time is the body adapts to that style of training and your gains will end. Adaptation is the beginning of the lack of muscle growth.
Whatever program that you decide to perform make sure that about every six to eight weeks you change it up. I have gained using four sets of 8 to 12 reps and I have also gained performing much higher reps.
Keep in mind you have many tools that can be manipulated for you to achieve your goals;
Number of sets
Number of reps
amount of rest in between sets
How fast or slow you are performing your reps
Different movements for the same body part
How many times you train per week
And of course don't forget a very important factor: nutrition and protein intake. If your goal is hypertrophy you need to consume high quality protein like eggs, meat, fish and of course milk. And make sure you take a high quality protein supplement. Biotest has a great one but there are others.
Remember to keep your body guessing. When your body adapts to your program, which takes anywhere from 6 to 8 weeks, it's time to change it up. That doesn't always mean changing your rep or set protocol. It could mean just changing your movements. But, keep in mind anything that shocks the body (in a positive way) will usually keep you growing!
Good Luck With Your Training,