Lets assume that all things being equal and that tension is equal to weight.

A string held at 20 lbs. by a physical weight will always be at 20lbs because the weight hasn't changed and nothing mechanical is locking the string at any point. As the string ages due to use or to constant tension the weight with gravity will continue to moderate the tension and pull the string so there is always 20lbs. on the string.

A string at 20lbs. and held there by a tuning machine will only stay at 20 lbs. just so long and then begin to lose tentsion because of use. The tuning machine being a fixed means of adding tension.

This discussion isn't going anywhere or has any deep purpose, it is just a "Wonder Me" kind of question.

Don