tone-uncage-fire,
the definitions weight and balance has provided are quite right. The theory you present is nice, but not grounded in practicality. I helped author a NASA report on limits, and had to carefully state that limits are mostly based on where the qualification test stopped. A limit is the maximum value for which safety and operability can be assured. A limit might be physical (stuff breaks above the limit) it might be practical (why bother to test farther, nobody goes there) and it might be economically set (since nobody wants more why pay to test more).
Of course, we poor folks have no way of knowing what reason was used, and nobody has a real idea how much above limit you can go before we read about it in the morning papers!