The thing with bottled nutes is that you are bypassing the soil food web and force feeding the plant. When you force feed a plant like this, it doesn't have a choice about taking up the nutrients, osmotic pressure forces the nutes into the roots. This is why you have to stop feeding and flush the excess salts out of the soil when feeding with bottled nutes.
With living soil, the plant produces exudates from the roots to attract and multiply the specific microbes necessary to produce the specific nutrients that the plant needs to grow to it's full genetic potential. Most of us experience fade towards the end of a run in living soil. IMO this isn't down lack of nutrients in the soil, rather the plant doesn't need to take nutes out of the soil anymore and starts using the easier accessed nutrients already stored in it's leaves. Horticulturalist's call this natural progression 'plant senescence' and it's probably part of the reason why we don't need to flush, the other being the lack of salt build up from using bottled products.