There are many goals to building one's body, many times it is the repetition that builds the strength and speed over larger quantities of weight.
Eventually the muscles atrophy with old age, and to maintain the muscle structure of a sculpted weightlifter is nearly impossible.
Most of your static exercises, such as pushups/squatthrusts/ kneebends are the key to stretching and strength. If you can lift 50 lbs 200 times verses lifting 200 lbs ten times, which do you think will benefit the body? My experience is that the higher repetitions create a much stronger body.
If you think that lifting heavy weights will give you strength, it will ... for a few years.
For my money, and strength that always surprises the buff weight lifter, you need to increase your aerobic and static strength.
(Static being the equal increase of small muscles such as muscles used in ballet stretches and repetitive tasks, not the reference to being still or dynamic tension.)