Not always.
There are tonnes of very strong guys out there who do not look good at all, from a bb'ing point of view, and they train for bb'ing.
And if your on enough drugs, you don't even have to train heavy.
As long as you are bettering your self each time you hit the gym then yes its true ,but that last bit is not true , if you are on alot of drugs you do train heavy(for you) because you can..taking drugs and training like a pussy = failure..Its what is heavy for you as an individual that could be 10kg or 100kg as long as you are trying to add more reps or weight each time then you are heading in the right direction.
If you are lifting the same weight for the same reps on any exercise that you were a year earlier then dont expect your muscles to change in size.
You are correct in some aspects of this post , there are some very strong bodybuilders out there but bodybuilding is not weightlifting but should be thought of as weight feeling as long as progressive resistence is useed.