Dude, I'm lazy. I have a bad back and really bending over with buckets of soil and going through the process is labor some and time consuming. Lets go through the process, first I have plants harvesting at different times. Which means I'm doing it regularly on top of spending a couple hours harvesting a couple plants. So I'm doing this process which is labor some, and takes about 15-20 minutes running water through the soil. Now I have to have an extra bin, which means space. I live where I grow, its not like I want my apartment to have containers of soil all over the place. So I have to do this each and every time, have an extra bin, lifting 3 gallon soaked buckets, and adding a timed process into my life. I'm not aiming for complete and utter maximization, I'm simply growing for myself. My goals are not commercial, and I agree I could save money by re using my soil. Due to my fucked spine, its easier on me and well worth paying $10/bag and a giant bag of perlite for $20 which will last me at least 6 months.
The focus is on using fertilizers and the costs associated to not understanding NPK, nutritional availability, and marketing. I mean just look at the difference of the websites and how they present the information on their products.
There is a charge in Happy Frog and Ocean Forest including the nitrates added using worm castings, but again, that doesn't make it a soil. Think of it as additives to an otherwise inert medium. It gets used up so quickly, once you get into the veg state.
To answer you last question, refer to my post or the following links:
http://www.jrpeters.com/Products/Jack-s-Classic/Citrus-FeED.html
http://www.jrpeters.com/Products/Jack-s-Classic/All-Purpose.html