The part about sitting on blocks has several good points , we have cutworms pretty bad at times here the concrete blocks stop them cold, fireants are also bad and with the pourous block a small amount of insecticide will soak in and stay a long time and it isnt in your growing soil.
After some of your responses I can see this may be another case of location sensitive, the ground where I live is black clay , rich as can be but turns to rock when it gets hot ,takes about five years of working in soil additives to start getting it mellow. This is Texas 105 in the summer and not much rain at times. This system stores water well and uses a whole lot less of it than trying to water the ground , plants go dormant above a 100 so with these raised beds I can move them under the trees in my back yard where it is from 5 to 15 degrees cooler.
There are a lot of advantages to this system for me , enough that this year my whole garden will be in boxes nothing in the ground.
Ron
You can have this garden on gravel rock concrete a patio ,well you get the ideal