That's really interesting - thanks for doing the footwork.
It makes me wonder about quality ...or, more specifically "quality". Since tanks failing is, if not rare, then uncommon (at least early in a tank's life before the silicone starts to rot away), is it really just the silicone that does the real work? It makes sense that a very slight glass angle wouldn't make much of a difference when you factor in such simple things as leaning heavily on one side when reaching down to the bottom of a filled tank.
My guess is that the unease people feel about DIY tanks is related to the fact that so few people know the basics of how to construct them. For example, do you place sides on top of the bottom pane, or next to the bottom pane? What seems obvious to critics is often not so obvious to the folks willing to get their hands dirty and give it a shot.
I can't remember seeing a thread talking about types and strength of silicone glue, other than your basic Home Depot varieties. Blazing, do you have any information about this?
Wow, I wish I knew of a good, cheap, local glass source. This could be a fun project - "Seriously, How Badly Do I Have to Construct a Tank for It to Fail?"