Marcus, you're right. That's basically all it is. The main advantages of the system are: 1. Hot air rises, so air is pulled in to the middle of the system from the bottom. (Oxygen is the rate limiting factor in vermicomposting.) This seems to be one of the best ways to get oxygen in throughout your bin (rather than just the top 6 inches or so.) 2. Harvesting is easier than with most systems. Worms go where the food is, so if your column of food is high enough, when you harvest the bottom, there are VERY few worms there to be removed from the compost.

By placing bins on top of the others eventually you just get a very dense and packed material that probably could even go anaerobic. I just posted pictures of my new flow through bin http://forums.gardenweb.com/forums/load/verm/msg0422570210660.html. What you are mentioning here is more of a stacking bin system. A stacking bin system can work but generally the top bin would not press on the contents of the bottom bin, it would just touch it so the worms would migrate upwards. The thing is the worms will decide where they will go and are probably staying put in the lower levels as there is enough food for them.

As far as the sides of barrel collapsing under weight using wire, cord or rope there is a way to solve that. You use a small piece of PVC pipe maybe 1/2" or so and cut them to length to be installed. The PVC pipes are cheap and you can cut them with a hack saw or a band saw easy. Also they will not rust and last as long as the barrel. Sample image below I will make PVC a "red color" for reference and black lines represents rope,wire or cord. Tie the rope into a knot at the end first, if it is a wire then make a loop whatever it takes to STOP the rope from pulling through that first hole it will be going in to on the barrel. So again pull that rope (cord or whatever) through the first hole of barrel into the barrel but now you thread it in and through your PVC pipe you have cut to proper size, go ahead and pull it through (push it with a clothes hanger wire if it bends) an as it pops out the other end of PVC then grab it and now you feed that out the other hole in the barrel, now completly through the barrel. Grab it and pull it tight and make a knot or secure it with a clamp like a snap tie. It won't come though because it has a knot on the other side right? And that PVC is ridged so it can not bend to easy so you end up with a stiff piece of "plastic" pipe inside instead of metal. So hen you secure that rope or cord or wire on the outsides just make sure you pull it as tight as it needs to be and then secure the outside ends. If rope (cord,wire) is pulled tight then that PVC has no place to go see? So no collapse on side of barrel at that point. You do all of them that way and the barrel sides can not come in on you now because all those PVC pipes will not bend. Grab a piece of 1 or 2 foot PVC pipe in store sometime and bend it, this will give you idea on how stiff you think you might need it.

I have a bin where vermicompost does not fall through 3" by 3" holes on it's own. I have a bin where vermicompost does not want to fall through 7" by 7" holes on it's own. When I can entice the vermicompost to fall through, flow through?, it wants to fall in a column from the bottom all the way to the top. My vermicompost is not reading the instructions of how I am imagining my flow through to work. Huge flowthrough systems solve this by using precomposted cow manure. This flow through concept has not caught on in my toss in an apple core, toss in an egg carton flow through system. I do get the benefit of air at the bottom of the system. Moving bins around with 3 and 7 inch holes in the bottom is always exciting. I see your system is attached to the base with ties. It would be cool if the base was inches bigger and you could push the bin around back and forth over the base to harvest. This would take the place of a harvest bar.