My perspective on Seaside may be a little different, because I still remember Avi trying out many of the same ideas in Ruby, and moving to Smalltalk (at least initially) because its continuations didn't leak memory like MRI's did. I also know from personal discussions that the Smallthought guys are very pragmatic about their tools: when Squeak/Seaside were the right tool, they used it, but when Ruby, Java, Javascript, or another language/framework made more sense, they weren't dogmatic about using it.

I'm not trying to downplay the importance of Smalltalk to DabbleDB, but it was just one piece of the puzzle. The same "use the right tool for the problem" attitude seems to be increasingly pervading Twitter these days, which I think has helped as much as anything else in their improved stability and scale over the last year or so.